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Chemical and Biological Technologies in Agriculture
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Lignin synthesis pathway in response to Rhizoctonia solani Kühn infection in potato (Solanum tuberosum L.)

Chemical and Biological Technologies in Agriculture volume 11, Article number: 135 (2024) Cite this article

Abstract

Potato black scurf caused by Rhizoctonia solani Kühn is widespread worldwide. The exploration and analysis of the infection mechanism of Rhizoctonia solani Kühn has important scientific significance to enhance the disease resistance of potato and other horticultural crops, and then break the restriction of fungal harm to agricultural production. The physiological and biochemical indexes and the expression levels of related genes were measured at 0, 1, 4, 8 and 16 days (T0, T1, T2, T3, T4) after inoculation with pathogenic bacteria. The results showed that the contents of L-phenylalanine ammonia-lyase (PAL), peroxidase (POD), lignin, total phenols (TP), and flavonoids increased significantly in potato after infection by Rhizoctonia solani Kühn, with the contents of PAL and POD reaching a peak at 8 d and then decreasing, and the contents of lignin and total phenols changing most significantly, reaching the highest levels at day 8 (T3) and day 16 (T4), respectively. During the infestation, the content of eight phenolic compounds increased, and the genes responsible for the lignin synthesis pathway were upregulated. However, in the later stage of infestation, the expression of two genes (PAL PG0031457 and PG2021549, HCT PG0014959, and COMT PG0011266) was down-regulated. In the correlation analysis, gene expression levels of all the genes, except POD (PG0005062), CCoAOMT (PG0018688), and COMT (PG0011266), were found to be positively correlated with the contents of lignin, total phenols, flavonoids, PAL, POD, and eight phenolic substances. Therefore, based on a sound understanding of the occurrence mechanism of Potato black scurf, this experiment analyzed the effect of Rhizoctonia solani Kühn infestation on the content of relevant metabolites in the lignin synthesis pathway as well as gene expression in potatoes, which provides a scientific basis for the prevention and control management of potato black scurf.

Graphical Abstract

Highlights

  1. 1.

    Increased accumulation of secondary metabolites in potato caused by infection of Rhizoctonia solani Kühn

  2. 2.

    The expression of genes related to lignin synthesis pathway increased rapidly after the potato was infected by Rhizoctonia solani Kühn

  3. 3.

    The activities of potato antioxidant enzymes changed significantly after pathogen infection

  4. 4.

    Lignin synthesis pathway plays an important role in potato response to Rhizoctonia solani Kühn infection

Background

Potato black scurf is a very aggressive soil-borne fungal disease caused by Rhizoctonia solani Kühn. The pathogenic fungus is highly saprophytic and survives for long periods of time in the soil [1]. It can infect over 260 plant species belonging to more than 66 families, with a preference for grasses, Solanaceae, legumes, and cruciferous crops [2]. The fungus relies on carrier residues and soil for transmission and has a high incidence of disease that continues to damage the crop throughout its reproductive life, and in severe cases can lead to the destruction of the entire field [3]. Potato has a long history of artificial cultivation, a wide range of cultivated qualities and a wide area of cultivation. It has grown to become the world's fourth-largest food crop and the number one non-cereal food crop in daily consumption [4,5,6]. In recent years, many potato growing areas have problems such as difficulty in stubble reversal, poor disease resistance, and improper fertilization. These factors exacerbate the infestation of potato by Rhizoctonia solani Kühn., resulting in the occurrence of symptoms such as cracks on the surface of potato tubers, rough skin, and moles [7]. A light degree of susceptibility to the disease can cause deformed potato nodules or the formation of aerial potatoes, while a heavy degree of susceptibility can lead to the growth of the potato plant being stunted, resulting in the death of the whole plant. Finally, the quality of potato is reduced and the commodity value of potato is affected [8,9,10].

Pathogenic fungi attacking plants trigger self-protection mechanisms in plants, including promotion of plant cell wall thickening, activation of defense genes, triggering of immune response, and elimination of superoxide and hydrogen peroxide [11, 12]. At the same time, the chitin oligomer produced by the fungus into the plant body is recognized by the pattern chitin receptors on the cell membrane of the plant, which also triggers an immune response. In this process, the phenylpropane biosynthesis pathway was activated, triggering the metabolism of phenylpropane and producing important intermediates such as phenolic metabolites. These intermediates further synthesize the downstream substance lignin, which fills the secondary layer of the cell wall and effectively enhances the plant's disease resistance and defense [13]. PAL is an important enzyme in the phenylpropane biosynthesis pathway, responsible for regulating the production of antimicrobial substances such as phenolics, flavonoids, and lignans [14]. It has been observed that during bacterial infestation, PAL activity is stimulated, leading to an increase in the production of antimicrobial substances in the cells. Additionally, PAL can also function as a defense enzyme in the plant disease resistance process [15, 16]. Peroxidase is an enzyme with antioxidant properties that plays a vital role in the final stage of lignin synthesis. According to a study by Jing et al., increasing the activity of peroxidase and catalase (CAT) can help remove excessive reactive oxygen species (ROS) quickly, which in turn helps in enhancing plant resistance [17]. The results of previous studies on disease resistance in sugarcane (Saccharum officinarum L.) indicate that increased CAT activity in disease-resistant varieties after pathogen infestation is one of the important mechanisms of disease resistance, and that enhanced antioxidant enzyme activity reduces the accumulation of hydrogen peroxide, thereby mitigating damage to plant cells and tissues. Plants produce secondary metabolites that are chemically resistant and can be used as a class of natural defense molecules against microorganisms, viruses, or as signaling substances that are directly involved in the process of disease resistance responses [18, 19]. The secondary metabolites of plants mainly include flavonoids and phenolics, terpenoids, nitrogenous alkaloids, and sulfur-containing compounds. Among them, total phenols are considered one of the major secondary metabolites in the plant kingdom and have been shown to play an important role in protecting plants from oxidative stress damage, regulating plant growth and development, and resisting external biotic and abiotic stresses [20]. Phenolic compounds are produced through the metabolic process of phenylpropane, manganic acid, and other pathways. These compounds can be used by plants to defend against viruses. Phenolic compounds can rapidly synthesize and polymerize in the cell wall, providing a defense mechanism [21, 22]. Flavonoids can also contribute to the destruction of pathogenic bacteria by interfering with their normal metabolism and structure. This promotes plant antimicrobial activity and helps to prevent pathogens from causing disease [23]. Moreover, flavonoids can act as signaling molecules that activate the signaling pathway related to plant defense and regulatory mechanisms. This can improve the plant’s resilience to stress and enhance its resistance to adversity [24].

With the increasing planting area, the scope of potato black scurf has been expanding under the influence of irrational farming systems, field management measures, poor planting environment, and uneven comprehensive production technology, resulting in potato yield reduction, quality degradation, storage difficulties, and decreased market competitiveness [25]. Therefore, this experiment aims to study the physiological and biochemical responses of potato tubers to Rhizoctonia solani Kühns infestation, and to explore the key indicators and physiological response mechanisms. At the same time, the relationship between related pathways and gene expression will be investigated in depth, which will provide a solid foundation for the discovery of resistant materials and disease-resistant breeding of potato, and promote the green, efficient and sustainable development of potato industry.

Materials and methods

Test material

For this particular experiment, the original seed of Longshu No. 7 was utilized as the experimental material and it was provided by Gansu Yihang Potato Technology Development Co., Ltd. (Lanzhou, Gansu). The Rhizoctonia solani Kühn was provided and preserved by the laboratory of Gansu Academy of Agricultural Sciences (GANAS).

Sampling methods

Firstly, the detoxified seedlings are cultivated by stem tip stripping, then refined and planted until the original seed tuber grows out. Secondly, choose healthy seed potatoes with healthy shape, consistent size, no damage in shape, and weight of about 30 g, wash the surface dirt with sterile water, disinfect with 75% alcohol solution, rinse with sterile water three times, and then dry. The infestation of the pathogen was carried out by perforation sterilization, using a sterile perforator of 3 × 3 mm size to make 3-mm-deep circular holes at the equatorial position of the seed potato, and then sucking up 20 μl of the suspension of the pathogen spores in the holes with a sterile pipette gun after 45 min of rest, and the control group was connected to the sterile ultrapure water. The treated materials were placed in black plastic bags and stored at 25 ℃ in an artificial climate incubator (RTOP-500Y) without light. At 0 d (T0), 1 d (T1), 4 d (T2), 8 d (T3), and 16 d (T4) after bacterial inoculation, the sample tissues were taken with a sterilized medical scalpel, and then wrapped in tin foil, frozen in liquid nitrogen for 5 min, and then quickly transferred to an ultra-low-temperature refrigerator (−80 ℃) for storage.

Determination of physiological indexes

Phenylalanine ammonia-lyase activity (PAL) activity and lignin content were measured by ultraviolet and visible spectrophotometry (UV–Vis), using PAL activity kit BC0210 and lignin content assay kit BC4200, respectively; peroxidase (POD) activity, flavonoid content, and total phenol content were measured by visible spectrophotometry, using peroxidase activity kit BC0090, Plant Flavonoid Content Determination Kit BC1330, Plant Total Phenol (TP) Content Detection Kit BC1340; all the above kits are provided by Beijing Solarbio Science&Technology Co., Ltd. (Beijing, China), and the test method is referred to in the kit instruction manual.

Determination of phenolic compounds content was carried out by High Performance Liquid Chromatography (Agilent 1200), following the method of Ayaz et al. with appropriate modifications [26]. The chromatographic column was Waters Symmetry® C18 (5 μm, 4.6 mm × 250 mm), and the mobile phases were 100% chromatographic grade methanol (A) and 0.5% glacial acetic acid (B) at a flow rate of 0.8 ml/min. The injection volume was 5 μL, and the procedure was repeated three times. Sinapic and caffeic acids were detected at 325 nm, ferulic acid at 322 nm, p-coumaric acid at 310 nm, cinnamic acid at 276 nm, coniferol alcohol at 263 nm, cinnamyl alcohol at 273 nm, and sinapyl alcohol at 322 nm. The phenolic compounds were quantified by comparing the retention times with those of the standards, and the contents of phenolic compounds in μg/g were calculated by the standard curve method under each treatment.

RNA extraction and reverse transcription

The preserved sample tissues were first extracted from RNA using the SteadyPure Universal RNA Extraction Kit (Accurate, Hunan, China) according to the manufacturer's instructions, RNA concentration was detected using the NanoDrop 2000, RNA integrity was detected using the Agilent Bioanalyzer 2100, and secondly, RNA was reverse-transcribed using the FastKing gDNA dispelling RT SuperMix (Tiangen, Beijing, China).

Quantitative real-time polymerase chain reaction (qRT-PCR)

Based on our previous study [27], we selected 16 mRNA for real-time fluorescence quantitative PCR (qRT-PCR) validation (Additional file 1). Actin was used as an internal reference gene. According to the manufacturer’s instructions, we used the TB Green Premix Ex Taq II Kit to detect cDNAs obtained on the fluorescent qPCR instrument. The relative expression of each gene tested was calculated according to the 2−ΔΔCt method [28]. Three biological replicates were performed for each set of experiments and three technical replicates were performed for each reaction. Primers used for qRT-PCR experiments are listed in Additional file 1.

Data analysis

Microsoft Excel 2016 software was used to organize the data, Origin 9.0 software was used for data graphing, SPSS 23.0 was used for statistics and analysis of the data, and analysis of variance (ANOVA) was used to detect differences between groups using LSD and SNK methods. The Pearson correlation coefficient was used to identify the correlation between the data, and P < 0.05 was considered statistically significant.

Results

Effects of Rhizoctonia solani Kühn infection on key physiological indexes of potato

After the infestation by Rhizoctonia solani Kühn, the content of TP in potato tubers showed an increasing trend with the increase of treatment time. The maximum value of TP in T4 treatment was 1.34 mg/g, which increased by 70% compared with T0, and T2, T3 and T4 treatments which were significantly higher than T0. The flavonoid content also increased gradually with the increase of infection time, and reached the maximum value of 2.07 mg/g on the 16th day of infection. In the process of infection by pathogens, lignin increased first and then decreased. Different from total phenols and flavonoids, lignin reached a maximum value of 134.55 mg/g after 8 h of infection, which increased by 66.51% compared with T0. POD plays a key role in the process of lignin synthesis. With the increase of treatment time, POD activity rose slowly at first and then decreased rapidly. At 8 days of infection, POD activity reached the maximum value, which increased by 84.19% compared with T0 treatment. PAL activity was significantly increased after pathogen infection. T3 treatment was significantly higher than other treatments, and compared with T0, PAL activity was increased by 81.53% (Fig. 1).

Fig. 1
figure 1

Effects of Rhizoctonia solani Kühn infection on key physiological indexes of potato. The error bar refers to the standard error. Different letters indicate significant differences at the P < 0.05 level

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Response of 8 phenolic metabolites in potato to Rhizoctonia solani Kühn infection

As shown in Fig. 2, with the extension of infection time, caffeic acid content in potato tubers showed an increasing trend with the increase of treatment time, and reached the maximum at day 16, increasing by 77.78% compared with T0. The contents of sinapic acid and sinapyl alcohol increased gradually with the extension of infection time, and the contents of sinapyl alcohol did not change significantly on the 4th and 8th day after infection. Sinapic acid reached the maximum value in the T4 treatment, which was significantly higher than that in other treatments (the maximum value of sinapyl alcohol was 8.3 μg/g), and T3 treatment was significantly higher than in T0. The overall change trend of coniferol content was not obvious, there was no significant difference between the treatments. The content of p-coumaric acid increased slowly at first and then decreased rapidly with the increase of infection time. The content of p-coumaric acid began to decrease on the 16th day of infection and was close to that on the 4th day. The content of the T3 treatment was significantly higher than that of other treatments, reaching a maximum value of 11.47 μg/g. The contents of cinnamyl alcohol and cinnamic acid increased rapidly with the time of infection and reached the maximum value on the 16th day after infection, and the contents of cinnamic acid showed a rapid trend. Ferulic acid content showed an increasing trend with the increase of treatment time after pathogen infection, but the overall change trend was not obvious, and the maximum value of T4 was 2.02 μg/g, which increased by 12.85% compared with T0.

Fig. 2
figure 2

Content of phenolic compounds in potato after infection by Rhizoctonia solani Kühn. Error bars refer to the standard error. Different letters indicate significant differences at the P < 0.05 level

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Fig. 3
figure 3

The expression of key genes in potato lignin and synthesis pathway. Error bars refer to the standard error. Different letters indicate significant differences at the P < 0.05 level

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Effects of Rhizoctonia solani Kühn infection on the expression of key genes in the lignin synthesis pathway of potato

Based on the physiological and biochemical characteristics and gene function analysis, we found that the lignin synthesis pathway plays an important role in the response of potato to pathogens, and the expression of related genes in the lignin synthesis pathway increases rapidly with the extension of infection time.

PAL-related genes (PG0031457, PG0023458, PG2021549) were significantly upregulated after treatment, and PG2021549 was the highest at 4 days of infection, and significantly higher than other treatments. The expression of PG0014223 was significantly upregulated and reached the maximum in T2 treatment. The expression levels of the two genes encoding HCT (PG0014959 and PG0014062) increased first and then decreased with the increase of infection time, and reached the maximum value on the 8th day of infection. Among the three genes encoding CAD (PG0005359, PG0031326, PG0031325), PG0005359 showed an ascending–descending–ascending trend after infection and finally reached the maximum value in T4, which was significantly higher than that in T0 treatment. We found that the expression levels of four genes related to POD (PG0011640, PG0015106, PG1025083, and PG0005062) were significantly upregulated, but the expression levels of PG0005062 reached the maximum on the first day after infection and then began to decline slowly. The expression levels of two genes related to CCoAOMT (PG0018688 and PG0002387) were upregulated, and the expression levels of PG0002387 and PG0011266 reached their highest values at T2, and were significantly higher than those of other treatments (Fig. 3).

Model of key pathway of potato response to Rhizoctonia solani Kühn infection

To investigate the regulatory role of the lignin synthesis pathway in potato infection by Rhizoctonia solani Kühn, a model was constructed. It has been shown that the lignin synthesis pathway plays an important role in the response to Potato black scurf (as depicted in Fig. 4). In this pathway, when plants are infected by pathogenic bacteria, PAL-related genes in the phenylpropane biosynthesis pathway are upregulated, which promotes the increase of PAL content. The switch of the phenylpropane biosynthesis pathway is turned on, and under the catalytic action of phenylalanine ammonia-lyase, It promotes the upregulated expression of cinnamic acid content and produces phenolic compounds such as p-coumaric acid, caffeic acid, ferulic acid and sinapic acid under the catalyst of CYP73A, resulting in the upregulated expression of 4-coumaric acid-CoA ligase (4CL) and hydroxycinnamyl transferase (HCT) related genes, forming corresponding aldehydes. The genes related to CAD and POD are activated to upregulate the expression of cinnamaldehyde (coniferaldehyde, caffeic aldehyde, sinapaldehyde, coumaric aldehyde) to the corresponding alcohols and accelerate the synthesis of lignin. In this way, we also found that the contents of coumaric acid, caffeic acid, ferulic acid, sinapic acid, and sinapyl alcohol began to be upregulated after infection, which enhanced the resistance of potatoes to Rhizoctonia solani Kühn.

Fig. 4
figure 4

Model of key pathway of potato response to Rhizoctonia solani Kühn infection Note: the solid black arrows represent direct products, and the dashed arrows represent indirect products

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Correlation analysis of key gene expression and physiological indexes

As shown in Fig. 5, there is a positive correlation between genes related to PAL, 4CL, HCT, and CAD and the contents of 8 phenolic compounds, lignin, total phenols, flavonoids, PAL, and POD in the phenylpropane biosynthesis pathway. Among them, two genes encoding PAL (PG0031457, PG0023458) and CAD (PG0031326, PG0031325) and one gene encoding POD (PG1025083) and CCoAOMT (PG0002387) were associated with total phenols, flavonoids, lignin and a variety of phenolic compounds In addition, the four genes with significant positive correlation in lignin content were derived from PAL, CAD and COMT (PG0031457, PG0031325, PG0002387 and PG0031457, respectively). Among the genes encoding POD and CCoAOMT, PG005062 and PG0002387 showed a significant negative correlation with the contents of cinnamic acid, cinnamyl alcohol, ferulic acid, sinapyl alcohol, caffeic acid, total phenolic and lignin, while the COMT-related gene PG0011266 showed a significant negative correlation with the content of coniferol alcohol.

Fig. 5
figure 5

Correlation analysis between related genes and secondary metabolites in lignin synthesis pathway

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Discussion

Rhizoctonia solani Kühn has a serious negative impact on the growth and development of potato, and the damage to the plant has gradually become a research hotspot. The phenylpropane biosynthesis pathway is one of the major pathways for the synthesis of secondary metabolites in plants, and the initiator phenylalanine (Phe) is catalyzed by enzymes such as phenylalanine deaminase, 4CL, and C4H to enter the downstream specific branching pathway to produce different phenylpropane-like metabolites [29]. The 4CL reaction produces coumaryl-CoA, ferulic acid-CoA, sinapyl-CoA, and 5-hydroxy ferulic acid-CoA, which undergoes a CCR reduction reaction and a CDA reaction to form lignin monomers. Finally, the enzymes peroxidase and laccase (LAC) contribute to the polymerization of the lignin monomers substances into the macromolecule lignin [30]. Potatoes that are infested with Rhizoctonia solani Kühn can stimulate an autoimmune reaction. Potato infested with Rhizoctonia solani Kühn stimulates autoimmune responses, synthesizes large amounts of p-coumaric acid through activation of phenylalanine deaminase, enhances its antimicrobial and anti-inflammatory effects, and inhibits the growth and spread of pathogenic bacteria. In addition, infestation promoted the synthesis of lignin and the production of peroxidase, the content of which was directly proportional to the plant’s stress resistance, helping to eliminate reactive oxygen radicals and modulate cell wall components, enhancing the mechanical strength and antimicrobial properties of the cell wall [31]. These mechanisms reduce the penetration of pathogenic bacteria into the plant cell wall, which in turn effectively prevents the proliferation and spread of pathogenic bacteria [32, 33]. In this experiment, the contents of PAL, POD, and lignin increased to different degrees with the increase of pathogen infestation time, which indicated that pathogen infestation stress would lead to the increase of induced defense enzyme activities and the enhancement of the antioxidant enzyme system's ability to scavenge ROS. Previous studies also confirmed the accuracy of the present results. For example, Li et al. inoculated the disease-resistant and disease-susceptible varieties of cotton with Verticillium wilt, respectively, and found significant differences in lignin content and phenylpropane metabolic pathway gene expression between the disease-resistant and susceptible varieties [34], In addition, Ma et al. evaluated the disease resistance of transgenic tobacco and found that tobacco plants with low lignin content were susceptible to Pseudomonas solanacearum, while tobacco plants with high lignin content were not susceptible to pathogen infection [35]. Funnell and Panka found that lignin could prevent pathogenic bacteria from infusing plants [32], and this process would increase PAL activity. In addition, after infection by pathogenic bacteria, the total phenol content increased significantly, and PPO activity also increased in this process [36]. Eynck et al. found that after Camelina sativa (L.) Crantz is inoculated with sclerotinia, the S-type lignin content of resistant variety 36,011 increased by 40% compared with susceptible variety 36012 [37].

Secondary metabolites are important products of plant adaptation to the environment during the evolutionary process, and play an important role in plant growth and development as well as in the response process to adversity stress [38, 39], and the invasion of pathogenic bacteria triggers the plant's defense mechanism, which manifests itself at the physiological and biochemical level in the production and accumulation of antimicrobial actives (terpenes, phenolics, and flavonoids) and antioxidant enzymes and other substances [40]. After entering plants, Rhizoctonia solani Kühn not only changes the types and biological activities of secondary metabolites in plants, but also regulates the synthesis and accumulation of these secondary metabolites by affecting the expression of related genes. Total phenols, flavonoids, and phenolic compounds, as important secondary metabolites, are involved in plant–pathogen interactions, and their content is closely related to plant disease resistance [41, 42]. Flavonoids can serve as a secondary antioxidant system within plant cells, and their biosynthesis is triggered when changes occur in the first line of defense against ROS, the antioxidant enzyme system. At the same time, phenolic compounds can also actively respond to pathogen stress by inhibiting pathogen growth and enhancing their antioxidant and free radical scavenging activities to enhance their resistance to pathogens [43, 44]. However, studies have found that the content of phenolic substances in plants is not directly related to resistance, but the induced changes of phenolic substances are closely related to disease resistance [45]. It has been reported that sorghum seeds, alfalfa, and other plants will produce a kind of flavonoids to resist the infection of pathogens after being infected by pathogens [22, 46, 47]. Yang et al. found in the study that flavonoids extracted from potato and onion could inhibit the germination and growth of Fusarium oxysporum spores [48]. Geng et al. found that flavonoids can effectively inhibit the expansion of pathogens in infected cells and the expansion of lesions [49]. After infecting apples of different resistant varieties with Botrytis cinerea, Ma et al. found that PAL, C4H, and 4CL showed higher activity in resistant varieties, and the content of phenolic metabolites was higher than that of susceptible varieties [50]. Singh et al. found that in tomatoes susceptible to early blight, the synthesis and accumulation of flavonoids and flavone in tomatoes were enhanced after infection with early blight, enabling plants to play a leading role in the defense against pathogen infection [51]. The results of this experiment were similar to previous studies. In this experiment, the contents of flavonoids and total phenols increased gradually with the extension of infection time, indicating that the response of total phenols and flavonoids to pathogens was gradually enhanced with the increase of infection time, reducing the damage to own cells. The content of ferulic acid did not change significantly with the infection time, and the other 7 phenolic compounds increased gradually with the increase of treatment time. The total content of the eight phenolic compounds was highest in cinnamyl alcohol, followed by p-coumaric and sinapic acids, and caffeic acid. The remaining three compounds had relatively low contents. Therefore, the accumulation of phenolic compounds after infection by pathogenic bacteria is an important characteristic of potato resistance to black scurf.

In the process of plant disease resistance, phenylalanine can be used as a series of disease-resistant metabolite precursors such as phenyl propyl, flavonoids, and cell wall lignin to resist the infection of pathogens in plants [52], and a series of secondary metabolites such as cinnamic acid and caffeic acid also plays a role as the precursors of lignin formation in plant defense. For example, when Fusarium graminearum infects wheat, the cinnamic amides (HCAAs) accumulated in Fusarium graminearum can be transported through cell membranes and act on the lignification of cell walls [53]. Secondly, caffeic acid, coumaric acid, ferulic acid, salicylic acid, and tannic acid in wheat have strong inhibitory activities on major proteins in Fusarium graminearum, and the inhibitory effects of caffeic acid, salicylic acid, and ferulic acid have been confirmed in some fungal growth inhibition experiments [54]. In this experiment, 3 PAL genes had the strongest correlation with the content of cinnamyl alcohol, 2 genes reached a significant level, 3 CAD genes had the strongest correlation with the content of p-coumaric acid, and 2 genes had a very significant correlation with the content of p-coumaric acid. It has been observed that pathogen infection can rapidly induce an increase in the activity of PAL and 4CL, leading to an increase in the content of cinnamic acid and ferulic acid. However, one POD gene and one CCoAOMT gene were negatively correlated with lignin, total phenols, flavonoids, PAL, POD, and 8 phenolic substances, indicating that the increase of gene expression level would also lead to the decrease of phenolic compounds content. Wei et al. also found that after sesame was infected with Fusarium oxysporum, genes related to the phenylpropane metabolic pathway were upregulated, including PAL, 4CL, CCoAMT, POD [55]. Jadhav et al. found that PAL gene expression in castor bean varieties resistant to Fusarium wilt disease increased with delayed infestation and was much higher than in susceptible varieties. Certain levels of ferulic acids and caffeic acids were also detected in resistant genotypes [56]; Zheng et al. in the study of resistance rape infection with Fusarium longisporum, it was found that PAL activity in resistant rape increased with the increase of infection time, and the expression levels of PAL, C4H, C3H, CCoAMT, CCR, CAD and POX genes related to lignin synthesis were upregulated [57]. The above experimental results further indicated that the propane biosynthesis pathway would be activated after pathogen infection, and related genes were also upregulated, which promoted potato response and resistance to the pathogen by increasing the activity of defense enzymes and producing a series of secondary metabolites. Therefore, the study of the interaction mechanism of Rhizoctonia solani Kühn on potato provides a more reliable basis for the prevention and control of potato black scurf in the future.

Conclusions

After infection by pathogenic bacteria, total phenols and flavonoids in potato reached the highest value at T4, while lignin, POD and PAL increased first and then decreased. The contents of 8 phenolic compounds generally increased, especially cinnamyl alcohol increased significantly, but ferulic acid did not change significantly. The expression of 16 genes related to lignin synthesis was upregulated with the increase of infection time. Correlation analysis showed that some genes were negatively correlated with the contents of lignin, total phenols, flavonoids, PAL, POD and 8 phenolic substances, such as PG0005062, PG0018688 and PG0011266, while others were positively correlated. Through the study of the infection mechanism of Rhizoctonia solani Kühn, the molecular mechanism of potato resistance response caused by pathogen infection was revealed, which is of great significance for the understanding of the interaction between potato and pathogen and the resistance mechanism, and provides a theoretical basis for breeding resistant varieties and improving the prevention and control ability of potato nigrum disease.

Availability of data and materials

The datasets generated and analysed during the current study are available in the NCBI repository,https://www.ncbi.nlm.nih.gov/sra/?term=SRP314907 , the accession number is SRP314907. The datasets used and analyzed in the current study are available from the corresponding author on reasonable request.

Abbreviations

PAL:

Phenylalanine ammonia lyase

POD:

Peroxidase

TP:

Total phenols

4CL:

4-Coumarate:CoA ligase

HCT:

Hydroxycinnamoyl transferase

CAD:

Cinnamyl alcohol dehydrogenase

CCoAOMT:

Caffeoyl-CoA O-methyltransferase

COMT:

Caffeic acid O-methyltransferase

Phe:

Phenylalanine

CCR:

Cinnamoyl-CoA reductase

CDA:

Cinnamoyl-CoA reductase

LAC:

Laccase

PPO:

Polyphenol oxidase

C4H:

Cinnamate 4-Hydroxylase

HCAAs:

Hydroxycinnamic acid amides

qRT-PCR:

Quantitative real-time polymerase chain reaction

C3H:

Cinnamate 3-Hydroxylase

POX:

Proline oxidase

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Acknowledgements

The authors would also like to thank the Charlesworth Group (https://www.cwauthors.com) for linguistic assistance during the preparation of this manuscript.

Funding

This work was supported by Doctoral Foundation of Gansu Academy of Agricultural Sciences (2023GAAS38); National Natural Science Foundation of China (32360488); Natural Science Foundation of Gansu Province (23JRRA1339); National Key R&D Program of China (2023YFD2302100).

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Authors and Affiliations

  1. Institute of Potato, Gansu Academy of Agricultural Sciences, Lanzhou, 730070, Gansu, China

    XinYu Yang, HePing Lv, YanPing Gao, YanBin Wu, FangFang Wang, Wu Zhang & HongJie Liang

  2. Horticulture College of Gansu Agricultural University, Lanzhou, 730070, Gansu, China

    Wangjun Zhang & YiChen Kang

  3. State Key Laboratory of Aridland Crop Science (Gansu Agricultural University), Lanzhou, 730070, Gansu, China

    YiChen Kang

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  1. XinYu Yang
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  8. Wu Zhang
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Contributions

Xinyu Yang: conceptualization, original draft preparation, funding acquisition. Wangjun Zhang: review and editing. HePing Lv: investigation. YanPing Gao: validation. YiChen Kang: visualization. YanBin Wu: supervision. FangFang Wang: methodology. Wu Zhang: formal analysis, project administration. HongJie Liang: data curation.

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Yang, X., Zhang, W., Lv, H. et al. Lignin synthesis pathway in response to Rhizoctonia solani Kühn infection in potato (Solanum tuberosum L.). Chem. Biol. Technol. Agric. 11, 135 (2024). https://doi.org/10.1186/s40538-024-00663-0

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