PAL-mediated SA biosynthesis pathway contributes to nematode resistance in wheat

The MdVQ37-MdWRKY100 complex regulates salicylic acid content and MdRPM1 expression to modulate resistance to Glomerella leaf spot in apples

Glomerella leaf spot (GLS), caused by the fungus Colletotrichum fructicola, is considered one of the most destructive diseases affecting apples. The VQ-WRKY complex plays a crucial role in the response of plants to biotic stresses. However, our understanding of the defensive role of the VQ-WRKY complex on woody plants, particularly apples, under biotic stress, remains limited. In this study, we elucidated the molecular mechanisms underlying the defensive role of the apple MdVQ37-MdWRKY100 module in response to GLS infection. The overexpression of MdWRKY100 enhanced resistance to C. fructicola, whereas MdWRKY100 RNA interference in apple plants reduced resistance to C. fructicola by affecting salicylic acid (SA) content and the expression level of the CC-NBS-LRR resistance gene MdRPM1. DAP-seq, Y1H, EMSA, and RT-qPCR assays indicated that MdWRKY100 inhibited the expression of MdWRKY17, a positive regulatory factor gene of SA degradation, upregulated the expression of MdPAL1, a key enzyme gene of SA biosynthesis, and promoted MdRPM1 expression by directly binding to their promotors. Transient overexpression and silencing experiments showed that MdPAL1 and MdRPM1 positively regulated GLS resistance in apples. Furthermore, the overexpression of MdVQ37 increased the susceptibility to C. fructicola by reducing the SA content and expression level of MdRPM1. Additionally, MdVQ37 interacted with MdWRKY100, which repressed the transcriptional activity of MdWRKY100. In summary, these results revealed the molecular mechanism through which the apple MdVQ37-MdWRKY100 module responds to GLS infection by regulating SA content and MdRPM1 expression, providing novel insights into the involvement of the VQ-WRKY complex in plant pathogen defence responses.

The genetic orchestra of salicylic acid in plant resilience to climate change induced abiotic stress: critical review

Climate change, driven by human activities and natural processes, has led to critical alterations in varying patterns during cropping seasons and is a vital threat to global food security. The climate change impose several abiotic stresses on crop production systems. These abiotic stresses include extreme temperatures, drought, and salinity, which expose agricultural fields to more vulnerable conditions and lead to substantial crop yield and quality losses. Plant hormones, especially salicylic acid (SA), has crucial roles for plant resiliency under unfavorable environments. This review explores the genetics and molecular mechanisms underlying SA's role in mitigating abiotic stress-induced damage in plants. It also explores the SA biosynthesis pathways, and highlights the regulation of their products under several abiotic stresses. Various roles and possible modes of action of SA in mitigating abiotic stresses are discussed, along with unraveling the genetic mechanisms and genes involved in responses under stress conditions. Additionally, this review investigates molecular pathways and mechanisms through which SA exerts its protective effects, such as redox signaling, cross-talks with other plant hormones, and mitogen-activated protein kinase pathways. Moreover, the review discusses potentials of using genetic engineering approaches, such as CRISPR technology, for deciphering the roles of SA in enhancing plant resilience to climate change related abiotic stresses. This comprehensive analysis bridges the gap between genetics of SA role in response to climate change related stressors. Overall goal is to highlight SA's significance in safeguarding plants and by offering insights of SA hormone for sustainable agriculture under challenging environmental conditions.

Genome-Wide Identification and Expression Profile Analysis of the Phenylalanine Ammonia-Lyase Gene Family in Hevea brasiliensis

The majority of the world's natural rubber comes from the rubber tree (Hevea brasiliensis). As a key enzyme for synthesizing phenylpropanoid compounds, phenylalanine ammonia-lyase (PAL) has a critical role in plant satisfactory growth and environmental adaptation. To clarify the characteristics of rubber tree PAL family genes, a genome-wide characterization of rubber tree PALs was conducted in this study. Eight PAL genes (HbPAL1-HbPAL8), which spread over chromosomes 3, 7, 8, 10, 12, 13, 14, 16, and 18, were found to be present in the genome of H. brasiliensis. Phylogenetic analysis classified HbPALs into groups I and II, and the group I HbPALs (HbPAL1-HbPAL6) displayed similar conserved motif compositions and gene architectures. Tissue expression patterns of HbPALs quantified by quantitative real-time PCR (qPCR) proved that distinct HbPALs exhibited varying tissue expression patterns. The HbPAL promoters contained a plethora of cis-acting elements that responded to hormones and stress, and the qPCR analysis demonstrated that abiotic stressors like cold, drought, salt, and H2O2-induced oxidative stress, as well as hormones like salicylic acid, abscisic acid, ethylene, and methyl jasmonate, controlled the expression of HbPALs. The majority of HbPALs were also regulated by powdery mildew, anthracnose, and Corynespora leaf fall disease infection. In addition, HbPAL1, HbPAL4, and HbPAL7 were significantly up-regulated in the bark of tapping panel dryness rubber trees relative to that of healthy trees. Our results provide a thorough comprehension of the characteristics of HbPAL genes and set the groundwork for further investigation of the biological functions of HbPALs in rubber trees.

Rice transcription factor OsNAC2 maintains the homeostasis of immune responses to bacterial blight

Rice (Oryza sativa) bacterial blight, caused by Xanthomonas oryzae pv. Oryzae (Xoo), threatens plant growth and yield. However, the molecular mechanisms underlying rice immunity against Xoo remain elusive. Here, we identified a NAC (NAM-ATAF-CUC) transcription factor OsNAC2 as a negative regulator in the resistance to bacterial blight disease in rice. Constitutive overexpression of OsNAC2 inhibited the expression of salicylic acid (SA) biosynthesis-related genes (i.e. isochorismate synthase 1 (OsICS1), phenylalanine ammonia lyase 3 (OsPAL3), etc.) with adverse impacts on the pathogenesis-related proteins (PRs) responses and compromised blight resistance. Moreover, OsNAC2 interacted with APETALA2/ethylene-responsive element binding protein (AP2/EREBP) transcription factor OsEREBP1 and possibly threatened its protein stability, destroying the favorable interaction of OsEREBP1-Xa21-binding protein OsXb22a in the cytoplasm during Xoo-induced infection. On the contrary, downregulation of OsNAC2 resulted in enhanced resistance to bacterial blight in rice without any growth or yield penalties. Our results demonstrated that OsNAC2 inhibits SA signaling and stably interacted with OsEREBP1 to impair disease resistance. This OsNAC2-OsEREBP1-based homeostatic mechanism provided insights into the competition between rice and bacterial pathogens, and it will be useful to improve the disease resistance of important crops through breeding.

Comparative transcriptome revealed the molecular responses of Aconitum carmichaelii Debx. to downy mildew at different stages of disease development

BACKGROUND

Aconitum carmichaelii Debx. has been widely used as a traditional medicinal herb for a long history in China. It is highly susceptible to various dangerous diseases during the cultivation process. Downy mildew is the most serious leaf disease of A. carmichaelii, affecting plant growth and ultimately leading to a reduction in yield. To better understand the response mechanism of A. carmichaelii leaves subjected to downy mildew, the contents of endogenous plant hormones as well as transcriptome sequencing were analyzed at five different infected stages.

RESULTS

The content of 3-indoleacetic acid, abscisic acid, salicylic acid and jasmonic acid has changed significantly in A. carmichaelii leaves with the development of downy mildew, and related synthetic genes such as 9-cis-epoxycarotenoid dioxygenase and phenylalanine ammonia lyase were also significant for disease responses. The transcriptomic data indicated that the differentially expressed genes were primarily associated with plant hormone signal transduction, plant-pathogen interaction, the mitogen-activated protein kinase signaling pathway in plants, and phenylpropanoid biosynthesis. Many of these genes also showed potential functions for resisting downy mildew. Through weighted gene co-expression network analysis, the hub genes and genes that have high connectivity to them were identified, which could participate in plant immune responses.

CONCLUSIONS

In this study, we elucidated the response and potential genes of A. carmichaelii to downy mildew, and observed the changes of endogenous hormones content at different infection stages, so as to contribute to the further screening and identification of genes involved in the defense of downy mildew.

Overexpression of GmPAL Genes Enhances Soybean Resistance Against Heterodera glycines

Soybean cyst nematode (Heterodera glycines, soybean cyst nematode [SCN]) disease adversely affects the yield of soybean and leads to billions of dollars in losses every year. To control the disease, it is necessary to study the resistance genes of the plant and their mechanisms. Isoflavonoids are secondary metabolites of the phenylalanine pathway, and they are synthesized in soybean. They are essential in plant response to biotic and abiotic stresses. In this study, we reported that phenylalanine ammonia-lyase (PAL) genes GmPALs involved in isoflavonoid biosynthesis, can positively regulate soybean resistance to SCN. Our previous study demonstrated that the expression of GmPAL genes in the resistant cultivar Huipizhi (HPZ) heidou are strongly induced by SCN. PAL is the rate-limiting enzyme that catalyzes the first step of phenylpropanoid metabolism, and it responds to biotic or abiotic stresses. Here, we demonstrate that the resistance of soybeans against SCN is suppressed by PAL inhibitor l-α-(aminooxy)-β-phenylpropionic acid (L-AOPP) treatment. Overexpression of eight GmPAL genes caused diapause of nematodes in transgenic roots. In a petiole-feeding bioassay, we identified that two isoflavones, daidzein and genistein, could enhance resistance against SCN and suppress nematode development. This study thus reveals GmPAL-mediated resistance against SCN, information that has good application potential. The role of isoflavones in soybean resistance provides new information for the control of SCN. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

The rhizobacterial strain, Pseudomonas putida AKMP7, causes conditional pathogenesis in Arabidopsis thaliana via negative regulation of salicylic acid signaling, under water stress

We have previously reported a phenomenon of "conditional pathogenesis", in which, a drought-tolerant rhizobacterium, Pseudomonas putida AKMP7, promotes plant growth under well-watered conditions, while, deteriorating plant health under water-stressed conditions, in Arabidopsis thaliana seedlings. To understand the molecular mechanisms behind this phenomenon, we studied the modulation of salicylic acid (SA) biosynthesis as well as SA-responsive gene expression, involved in systemic acquired resistance (SAR), in A. thaliana, by AKMP7, under well-watered and water-stressed conditions. We found that, the plant SA levels were upregulated by AKMP7, both under, well-watered as well as water-stressed conditions. However, the SA signaling gene, Non-expressor of Pathogenesis Related gene 1 (NPR1) and Pathogenesis Related gene 1 (PR1) were upregulated under well-watered conditions and suppressed under water-stress, in AKMP7 inoculated seedlings. To understand the reason for this, we studied the expression of NPR4, a negative regulator of NPR1, and, NPR3, a negative regulator of PR1. We observed that, AKMP7 suppresses NPR1 and, consequently, PR1 genes, by upregulating NPR4 under water stress. To understand the potential role of NPR4 in conditional-pathogenesis, we performed physiological studies with NPR4 knockout mutants of A. thaliana and found that the NPR4 mutants did not exhibit any signs of the characteristic growth retardation caused by AKMP7 inoculation, under water stress. Preliminary studies with the model pathogen, Pseudomonas syringae, indicate that AKMP7 may lead to enhanced disease suppression under well-watered conditions, but not under water-stress. Taken together, our data suggest that, AKMP7 causes conditional pathogenesis by an overall compromise in plant immune response under water-stress.

Genome-wide identification and expression analyses of phenylalanine ammonia-lyase gene family members from tomato (Solanum lycopersicum) reveal their role in root-knot nematode infection

Phenylalanine ammonia-lyase (PAL) is a key enzyme and rate-limiting enzyme of phenylpropanoid metabolism, which is a very important pathway in plants, and the secondary products it produces play an important role in plant growth and development, disease resistance, and stress resistance responses. However, PALs still lack systematic characterization in tomato. Based on a bioinformatics methods, PAL family genes were identified and characterized from tomato. qRT-PCR was used to study the expression of PAL genes in cultivated tomato after root-knot nematode infection. In this study, 14 and 11 PAL genes were identified in cultivated and wild tomatoes, and phylogenetic analysis classified them into three subfamilies, with different subfamilies of PAL proteins evolving in different directions in monocotyledonous and dicotyledonous plants. The extensive presence of stress, growth, hormone, and light response elements in the promoter sequences of SlPAL (Solanum lycopersicum) and SpenPAL (Solanum pennellii) genes suggests that this family has a critical role in abiotic stress. Collinearity indicates that members of the tomato and Arabidopsis PAL genes family are from the same ancestor, and the SlPAL10 gene is directly homologous to monocotyledonous rice and maize, suggesting that the SlPAL10 gene was present before monocotyledonous differentiation. Two co-expressed gene modules containing PAL genes were screened by WGCNA, and the core genes in the network were mined and functionally annotated by calculating the connectivity of genes within the modules. In addition, the expression of some genes changed significantly after root-knot nematode infection, with up-regulation of 4 genes and down-regulation of 3 genes. This result provides a data reference for the study of PAL family gene functions in tomato, and also provides a potential application for the subsequent selection of PAL genes in tomato for root-knot nematode resistance.

Comparative analysis of Fusarium crown rot resistance in synthetic hexaploid wheats and their parental genotypes

BACKGROUND

Fusarium crown rot (FCR) is a chronic disease of cereals worldwide. Compared with tetraploid wheat, hexaploid wheat is more resistant to FCR infection. The underlying reasons for the differences are still not clear. In this study, we compared FCR responses of 10 synthetic hexaploid wheats (SHWs) and their tetraploid and diploid parents. We then performed transcriptome analysis to uncover the molecular mechanism of FCR on these SHWs and their parents.

RESULTS

We observed higher levels of FCR resistance in the SHWs compared with their tetraploid parents. The transcriptome analysis suggested that multiple defense pathways responsive to FCR infection were upregulated in the SHWs. Notably, phenylalanine ammonia lyase (PAL) genes, involved in lignin and salicylic acid (SA) biosynthesis, exhibited a higher level of expression to FCR infection in the SHWs. Physiological and biochemical analysis validated that PAL activity and SA and lignin contents of the stem bases were higher in SHWs than in their tetraploid parents.

CONCLUSION

Overall, these findings imply that improved FCR resistance in SHWs compared with their tetraploid parents is probably related to higher levels of response on PAL-mediated lignin and SA biosynthesis pathways.

Effect of Pochonia chlamydosporia Endophytism and Meloidogyne incognita Parasitism on WRKYs and Defense Gene Expression in Tomato Roots

The expression of WRKY transcription factors and plant defense-related genes was studied in the roots of Apulian tomato (Solanum lycopersicum) cv Regina di Fasano (accessions MRT and PLZ) endophytically colonized by Pochonia chlamydosporia and parasitized or not by the root-knot nematode (RKN) Meloidogyne incognita. The effect on plant growth, nematode parasitism and histological aspect of the interaction were considered. The association of P. chlamydosporia with RKN-parasitized MRT plants increased the total biomass and shoot fresh weight in comparison with healthy plants and with those only parasitized by RKN, without the endophyte. However, the PLZ accession showed no significant difference in the observed biometric parameters. The number of RKN-induced galls per plant was not affected by endophytism eight days after inoculation. No histological changes were observed in the nematode feeding sites in the presence of the fungus. Gene expression analysis showed an accession-specific response to P. chlamydosporia with differential activation of WRKY-related genes. No significant change was found for WRKY76 expression in nematode-parasitized plants compared with control roots, confirming cultivar susceptibility. Data indicate genotype-specific responses of the WRKY genes to parasitism examined in roots with nematodes and/or endophytic P. chlamydosporia. At 25 days post-inoculation with P. chlamydosporia, no significant difference was observed in the expression of defense-related genes in both accessions, suggesting that salicylic acid (SA) (PAL and PR1) and jasmonate (JA) related genes (Pin II) are not active during endophytism.

Salicylic acid interacts with other plant growth regulators and signal molecules in response to stressful environments in plants

Salicylic acid (SA) is one of the potential plant growth regulators (PGRs) that regulate plant growth and development by triggering many physiological and metabolic processes. It is also known to be a crucial component of plant defense mechanisms against environmental stimuli. In stressed plants, it is documented that it can effectively modulate a myriad of metabolic processes including strengthening of oxidative defense system by directly or indirectly limiting the buildup of reactive nitrogen and oxygen radicals. Although it is well recognized that it performs a crucial role in plant tolerance to various stresses, it is not fully elucidated that whether low or high concentrations of this PGR is effective to achieve optimal growth of plants under stressful environments. It is also not fully understood that to what extent and in what manner it cross-talks with other potential growth regulators and signalling molecules within the plant body. Thus, this critical review discusses how far SA mediates crosstalk with other key PGRs and molecular components of signalling pathways mechanisms, particularly in plants exposed to environmental cues. Moreover, the function of SA exogenously applied in regulation of growth and development as well as reinforcement of oxidative defense system of plants under abiotic stresses is explicitly elucidated.

Metabolites and Plant Hormones Related to the Resistance Response to Feeding Stimulation and Leaf Clipping Control in Chinese Pine (Pinus tabuliformis Carr.)

This experiment was conducted to define changes in metabolic pathways in response to mandibulate insect feeding and to provide a reference for further investigation of the molecular mechanisms underlying the development of conifer resistance. Chinese pine (Pinus tabuliformis Carr.) in good growth status in natural condition was chosen for stimulation by 10 pine caterpillars (Dendrolimus tabulaefomis Tsai et Liu) as feeding stimulation (FS), leaf clipping control (LCC) as mechanical damage, and CK group (with no treatment) (recorded as 0 h). The metabolome and total flavonoid content were measured in the needles at 0, 2, and 8 h after treatment. Plant hormones were measured with needles at 0, 0.5, 1, 1.5, 2, 4, 6, and 8 h after different treatments. The results show that a total of 30.8% flavonoids are identified by metabolomics analysis. Compared with leaf clipping control, feeding stimulation of Chinese pine caterpillars significantly induced the upregulation of metabolites in the flavonoid pathway in Chinese pine, and the plant hormones JA and IAA showed expression trends consistent with those of the metabolome. According to the biological processes of the four plant hormones involved, JA and SA are mostly involved in resistance formation, and in this study, both of them also have fluctuating expressions influenced by feeding stimulation, while the expressions of the growth-related hormones IAA and ABA have no significant changes at other time points except for 1 h after treatment. Thus, the flavonoid pathway is one of the main pathways involved in resistance formation in conifers, and JA and IAA are involved in the formation of resistance.

Phylogenomic analysis of phenylalanine ammonia-lyase (PAL) multigene family and their differential expression analysis in wheat (Triticum aestivum L.) suggested their roles during different stress responses

Phenylalanine ammonia-lyase (PAL) is a key enzyme in the phenylalanine metabolism pathway and plays an important role in plant growth and stress response. It has been widely reported in plants, but less studied in wheat. In this study, 54 PAL genes were identified in the wheat genome. Based on phylogenetic analysis, the 54 TaPAL genes were divided into four groups (I, II, III, and IV). Then, the expression levels of TaPALs under biotic stresses were analyzed by transcriptome data analysis. The results showed that 31 genes were up-regulated and one gene was down-regulated after inoculation with Fusarium graminearum, 11 genes were up-regulated and 14 genes were down-regulated after inoculation with Puccinia striiformis, and 32 up-regulated and three down-regulated genes after inoculation with powdery mildew. The expression patterns of the five TaPALs were further analyzed by qRT-PCR. After inoculation with F. graminearum, the expression levels of five TaPALs were up-regulated. However, the TaPALs (expect TaPAL49) were down-regulated when inoculated with P. striiformis. Finally, the functions of TaPAL32 and TaPAL42 in resistance of wheat to the stripe rust were further analyzed by virus induced gene silencing (VIGS) assays. The results showed that the disease severity of TaPAL32 and TaPAL42 silenced plants was higher than that of control plants at 14 days after inoculation. It indicated that these two genes played a positive role in wheat stripe rust resistance. This study provided new evidence support for the functional study of PAL genes in wheat, and provided potential application value for the breeding of wheat resistant varieties.

The biochemical changes in two moderately resistant and highly susceptible tomato cultivars at the later stages of Meloidogyne javanica infection

The most effective method of managing root-knot nematodes is employing resistant and tolerant cultivars. Investigating biochemical changes can help determine the cause of resistance or susceptibility of plants to nematodes. In this study, resistance levels of some tomato cultivars, ‘ALYSTE F-1’, ‘ARYZA F-1’, ‘Early Urbana’, ‘Rutgers’, ‘Dutch Mobil’ and ‘Hungarian Mobil’, were evaluated based on nematode reproduction indices under glasshouse conditions. After selecting the most susceptible and resistant cultivar, comparisons of activity of defence enzymes (guaiacol peroxidase, catalase, ascorbate peroxidase, superoxide dismutase, polyphenol oxidase and phenylalanine ammonia-lyase), and phenolic and lignin contents in leaves and roots were investigated. Analysis of nematode reproductive traits revealed that ‘ALYSTE F-1’ had the lowest number of galls per root system, egg masses per root system, eggs per root system, and second-stage juveniles per 1.5 kg of soil and, consequently, the lowest number of nematode populations. Finally, ‘ALYSTE F-1’ and ‘Dutch Mobil’ (based on reproduction factor, gall index and resistance index) were selected as moderately resistant and highly susceptible cultivars, respectively, for biochemical analysis. Biochemical analysis of leaves and roots showed that most of the defence compounds in ‘ALYSTE F-1’ were higher than ‘Dutch Mobil’. These results also showed that ‘ALYSTE F-1’ reacted to nematode attack more rapidly than ‘Dutch Mobil’.

Systemic acquired resistance-associated transport and metabolic regulation of salicylic acid and glycerol-3-phosphate

Systemic acquired resistance (SAR), a type of long-distance immunity in plants, provides long-lasting resistance to a broad spectrum of pathogens. SAR is thought to involve the rapid generation and systemic transport of a mobile signal that prepares systemic parts of the plant to better resist future infections. Exploration of the molecular mechanisms underlying SAR have identified multiple mobile regulators of SAR in the last few decades. Examination of the relationship among several of these seemingly unrelated molecules depicts a forked pathway comprising at least two branches of equal importance to SAR. One branch is regulated by the plant hormone salicylic acid (SA), and the other culminates (based on current knowledge) with the phosphorylated sugar derivative, glycerol-3-phosphate (G3P). This review summarizes the activities that contribute to pathogen-responsive generation of SA and G3P and the components that regulate their systemic transport during SAR.

Unraveling Microbial Volatile Elicitors Using a Transparent Methodology for Induction of Systemic Resistance and Regulation of Antioxidant Genes at Expression Levels in Chili against Bacterial Wilt Disease

Microbial volatiles benefit the agricultural ecological system by promoting plant growth and systemic resistance against diseases without harming the environment. To explore the plant growth-promoting efficiency of VOCs produced by Pseudomonas fluorescens PDS1 and Bacillus subtilis KA9 in terms of chili plant growth and its biocontrol efficiency against Ralstonia solanacearum, experiments were conducted both in vitro and in vivo. A closure assembly was designed using a half-inverted plastic bottle to demonstrate plant–microbial interactions via volatile compounds. The most common volatile organic compounds were identified and reported; they promoted plant development and induced systemic resistance (ISR) against wilt pathogen R. solanacearum. The PDS1 and KA9 VOCs significantly increased defensive enzyme activity and overexpressed the antioxidant genes PAL, POD, SOD, WRKYa, PAL1, DEF-1, CAT-2, WRKY40, HSFC1, LOX2, and NPR1 related to plant defense. The overall gene expression was greater in root tissue as compared to leaf tissue in chili plant. Our findings shed light on the relationship among rhizobacteria, pathogen, and host plants, resulting in plant growth promotion, disease suppression, systemic resistance-inducing potential, and antioxidant response with related gene expression in the leaf and root tissue of chili.

How do plants defend themselves against pathogens-Biochemical mechanisms and genetic interventions

In agro-ecosystem, plant pathogens hamper food quality, crop yield, and global food security. Manipulation of naturally occurring defense mechanisms in host plants is an effective and sustainable approach for plant disease management. Various natural compounds, ranging from cell wall components to metabolic enzymes have been reported to protect plants from infection by pathogens and hence provide specific resistance to hosts against pathogens, termed as induced resistance. It involves various biochemical components, that play an important role in molecular and cellular signaling events occurring either before (elicitation) or after pathogen infection. The induction of reactive oxygen species, activation of defensive machinery of plants comprising of enzymatic and non-enzymatic antioxidative components, secondary metabolites, pathogenesis-related protein expression (e.g. chitinases and glucanases), phytoalexin production, modification in cell wall composition, melatonin production, carotenoids accumulation, and altered activity of polyamines are major induced changes in host plants during pathogen infection. Hence, the altered concentration of biochemical components in host plants restricts disease development. Such biochemical or metabolic markers can be harnessed for the development of "pathogen-proof" plants. Effective utilization of the key metabolites-based metabolic markers can pave the path for candidate gene identification. This present review discusses the valuable information for understanding the biochemical response mechanism of plants to cope with pathogens and genomics-metabolomics-based sustainable development of pathogen proof cultivars along with knowledge gaps and future perspectives to enhance sustainable agricultural production.

Monitoring of Host Suitability and Defense-Related Genes in Wheat to Bipolaris sorokiniana

Spot blotch caused by Bipolaris sorokiniana is a destructive disease of wheat worldwide. This study investigated the aggressiveness of B. sorokiniana isolates from different wheat-growing areas of Bolu province in Turkey on the cultivar Seri-82. Host susceptibility of 55 wheat cultivars was evaluated against the most aggressive isolate. Our results indicated that the cultivars Anafarta and Koç-2015 were the most resistant. A specific and sensitive qPCR assay was developed for detecting the pathogen in plant tissues and evaluating wheat plants with different resistance levels. Three primer sets, BsGAPDHF/BsGAPDHR, BsITSF/BsITSR, and BsSSUF/BsSSUR, were designed based on glyceraldehyde-3-phosphate dehydrogenase, internal transcribed spacers, and 18S rRNA loci of B. sorokiniana with detection limits of 1, 0.1, and 0.1 pg of pathogen DNA, respectively. The qPCR assay was highly sensitive and did not amplify DNA from the other closely related fungal species and host plants. The protocol differentiated wheat plants with varying degrees of resistance. The assay developed a useful tool for the quantification of the pathogen in the early stages of infection and may provide a significant contribution to a more efficient selection of wheat genotypes in breeding studies. In the present study, expression levels of PR proteins, phenylalanine ammonia-lyase, catalase, ascorbate peroxidase, and superoxide dismutase enzymes were upregulated in Anafarta (resistant) and Nenehatun (susceptible) cultivars at different post-infection time points, but more induced in the susceptible cultivar. The results showed considerable variation in the expression levels and timing of defense genes in both cultivars.