SlWRKY30 and SlWRKY81 synergistically modulate tomato immunity to <i>Ralstonia solanacearum</i> by directly regulating <i>SlPR-STH2</i>

Abstract

Bacterial wilt is a devastating disease of tomato (<i>Solanum lycopersicum</i>) caused by <i>Ralstonia solanacearum</i> that severely threatens tomato production. Group III WRKY transcription factors (TFs) are implicated in the plant response to pathogen infection; however, their roles in the response of tomato to <i>R. solanacearum</i> infection (RSI) remain largely unexplored. Here, we report the crucial role of SlWRKY30, a group III SlWRKY TF, in the regulation of tomato response to RSI. <i>SlWRKY30</i> was strongly induced by RSI. <i>SlWRKY30</i> overexpression reduced tomato susceptibility to RSI, and also increased H₂O₂ accumulation and cell necrosis, suggesting that SlWRKY30 positively regulates tomato resistance to RSI. RNA sequencing and reverse transcription-quantitative PCR revealed that <i>SlWRKY30</i> overexpression significantly upregulated pathogenesis-related protein (<i>SlPR-STH2</i>) genes <i>SlPR-STH2a</i>, <i>SlPR-STH2b</i>, <i>SlPR-STH2c</i>, and <i>SlPR-STH2d</i> (hereafter <i>SlPR-STH2a</i>/<i>b</i>/<i>c</i>/<i>d</i>) in tomato, and these <i>SlPR-STH2</i> genes were directly targeted by SlWRKY30. Moreover, four group III WRKY proteins (SlWRKY52, SlWRKY59, SlWRKY80, and SlWRKY81) interacted with SlWRKY30, and <i>SlWRKY81</i> silencing increased tomato susceptibility to RSI. Both SlWRKY30 and SlWRKY81 activated <i>SlPR-STH2a</i>/<i>b</i>/<i>c</i>/<i>d</i> expression by directly binding to their promoters. Taking these results together, SlWRKY30 and SlWRKY81 synergistically regulate resistance to RSI by activating <i>SlPR-STH2a</i>/<i>b</i>/<i>c</i>/<i>d</i> expression in tomato. Our results also highlight the potential of <i>SlWRKY30</i> to improve tomato resistance to RSI via genetic manipulations.