Tomato RAV transcription factor is a pivotal modulator involved in the AP2/EREBP-mediated defense pathway

Ralstonia solanacearum is the causal agent of bacterial wilt (BW), one of the most important bacterial diseases worldwide. We used cDNA microarray to survey the gene expression profile in transgenic tomato overexpressing Arabidopsis CBF1 (AtCBF1) that confers tolerance to BW. The disease-resistant phenotype is correlated with constitutive expression of the related-to-ABI3/VP1 (RAV) transcription factor, ethylene-responsive-factor (ERF) family genes, and several pathogenesis-related (PR) genes. Using a transient assay system, we show that tomato RAV2 (SlRAV2) can transactivate the reporter gene driven by the SlERF5 promoter. Virus-induced gene silencing (VIGS) of SlERF5 and SlRAV2 in AtCBF1 transgenic and BW-resistant cultivar H7996 plants gave rise to plants with enhanced susceptibility to BW. Constitutive overexpression of SlRAV2 in transgenic tomato plants induced expression of SlERF5 and PR5 genes and increased BW tolerance, while knockdown expression of SlRAV2 inhibited SlERF5 and PR5 gene expression under pathogen infection and significantly decreased BW tolerance. In addition, transgenic tomato overexpressing SlERF5 also accumulated higher levels of PR5 transcripts and displayed better tolerance to pathogen than wild-type plants. From these results, we conclude that SlERFs may act as intermediate transcription factors between AtCBF1 and PR genes via SlRAV in tomato, which results in enhanced tolerance to BW.