WRKY1 acts as a key component improving resistance against Alternaria solani in wild tomato, Solanum arcanum Peralta.

Balkrishna A Shinde,Ashok P Giri,Avinash C Kamble,Asaph Aharoni,Khalid Hussain,Bhushan B Dholakia

doi:10.1111/pbi.12892

Abstract

SummaryEarly 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.

Highlights

Plants have evolved diverse defence mechanisms to protect themselves against pathogen attack
Molecular cascades operating during Early blight (EB) resistance in such wild tomato against A. solani are not fully understood
From 886 coexpressed genes (CEG) with significant gene ontology (GO) terms, 306 genes indicated GO terms related to defence [i.e. response to stimulus (156 genes), immune system process (35 genes) and biological regulation (114 genes)] (Figure S1; Table S4)

Summary

Introduction

Plants have evolved diverse defence mechanisms to protect themselves against pathogen attack. Activated defence responses are mediated by complex signalling pathways affecting numerous cellular and molecular processes that lead to resistance These include generation of reactive oxygen species, cell wall lignification, accumulation of antimicrobial compounds and activation of defence-related genes (Durrant and Dong, 2004; Hammond-kosack and Jones, 1996; Jones and Dangl, 2006; Seo and Choi, 2015). These host responses to pathogen invasion are mediated by phytohormones such as salicylic acid (SA), jasmonic acid (JA) and ethylene (ET) (Bakshi and Oelmuller, 2014; Pieterse et al, 2012). These boxes are found in clusters within the short stretches in promoters indicating potential synergistic interactions of different WRKYs (Dong et al, 2003; Eulgem et al, 1999; Eulgem and Somssich, 2007)

Results

Discussion

Conclusion