RESUMEN
To elucidate the role of the phenylpropanoid pathway in the expression of resistance during compatible and incompatible interactions between pigeon pea and wilt-causing vascular pathogen Fusarium udum, we estimated the total phenol content, lignin, phenolic acids and activity of enzymes involved in lignin polymerization of monolignols and examined the expression pattern of lignin biosynthesis genes. Our results demonstrated a higher accumulation of free and cell wall-bound phenolics and total lignin content in the highly resistant pigeon pea genotype ICP 14623 as compared to susceptible genotype ICP 14166. An increased activity of phenylpropanoid pathway-associated defense enzymes such as Phenylalanine ammonia-lyase, polyphenol oxidase, ascorbate and guaiacol- dependent peroxidases in resistant pigeon pea genotypes suggests their role in resistance. Moreover, analysis of lignin biosynthesis genes revealed their differential expression during resistant and susceptible interactions, revealed their crucial role in imparting resistance against wilt. Overall, our results indicated the role of physical and biochemical components of the phenylpropanoid pathway in the expression of resistance in pigeon pea against Fusarium wilt.
Asunto(s)
Cajanus , Fusarium , Lignina , Cajanus/genética , Vías Biosintéticas , Fenilanina Amoníaco-Liasa/genética , Enfermedades de las Plantas/genéticaRESUMEN
Early blight (EB), caused by Alternaria solani, is a major threat to global tomato production. In comparison with cultivated tomato (Solanum lycopersicum), a wild relative, S. arcanum exhibits strong resistance against EB. However, molecular cascades operating during EB resistance in wild or cultivated tomato plants are largely obscure. Here, we provide novel insight into spatio-temporal molecular events in S. arcanum against A. solani. Transcriptome and co-expression analysis presented 33-WRKYs as promising candidates of which 12 SaWRKYs displayed differential expression patterns in resistant and susceptible accessions during EB disease progression. Among these, SaWRKY1 exhibited induced expression with significant modulation in xyloglucan endotrans hydrolase 5 (XTH5) and MYB2 expressions that correlated with the disease phenotypes. Electro-mobility shift assay confirmed physical interaction of recombinant SaWRKY1 to SaXTH5 and SaMYB2 promoters. Comparative WRKY1 promoter analysis between resistant and susceptible plants revealed the presence of crucial motifs for defence mechanism exclusively in resistant accession. Additionally, many defence-related genes displayed significant expression variations in both the accessions. Further, WRKY1 overexpressing transgenic plants exhibited higher levels of EB resistance while RNAi silencing lines had increased susceptibility to A. solani with altered expression of XTH5 and MYB2. Overall, these findings demonstrate the positive influence of WRKY1 in improving EB resistance in wild tomato and this could be further utilized as a potential target through genetic engineering to augment protection against A. solani in crop plants.
Asunto(s)
Alternaria/patogenicidad , Enfermedades de las Plantas/microbiología , Proteínas de Plantas/metabolismo , Plantas Modificadas Genéticamente/metabolismo , Plantas Modificadas Genéticamente/microbiología , Solanum lycopersicum/microbiología , Solanum/microbiología , Regulación de la Expresión Génica de las Plantas , Proteínas de Plantas/genéticaRESUMEN
KEY MESSAGE: Exploration with high throughput leaf metabolomics along with functional genomics in wild tomato unreveal potential role of steroidal glyco-alkaloids and phenylpropanoids during early blight resistance. Alternaria solani severely affects tomato (Solanum lycopersicum L.) yield causing early blight (EB) disease in tropical environment. Wild relative, Solanum arcanum Peralta could be a potential source of EB resistance; however, its underlying molecular mechanism largely remains unexplored. Hence, non-targeted metabolomics was applied on resistant and susceptible S. arcanum accessions upon A. solani inoculation to unravel metabolic dynamics during different stages of disease progression. Total 2047 potential metabolite peaks (mass signals) were detected of which 681 and 684 metabolites revealed significant modulation and clear differentiation in resistant and susceptible accessions, respectively. Majority of the EB-triggered metabolic changes were active from steroidal glycol-alkaloid (SGA), lignin and flavonoid biosynthetic pathways. Further, biochemical and gene expression analyses of key enzymes from these pathways positively correlated with phenotypic variation in the S. arcanum accessions indicating their potential role in EB. Additionally, transcription factors regulating lignin biosynthesis were also up-regulated in resistant plants and electrophoretic mobility shift assay revealed sequence-specific binding of rSaWRKY1 with MYB20 promoter. Moreover, transcript accumulation of key genes from phenylpropanoid and SGA pathways along with WRKY and MYB in WRKY1 transgenic tomato lines supported above findings. Overall, this study highlights vital roles of SGAs as phytoalexins and phenylpropanoids along with lignin accumulation unrevealing possible mechanistic basis of EB resistance in wild tomato.