RAV transcription factors are essential for disease resistance against cassava bacterial blight via activation of melatonin biosynthesis genes

Abstract With 1 AP 2 domain and 1 B3 domain, 7 Me RAV s in apetala2/ethylene response factor ( AP 2/ ERF ) gene family have been identified in cassava. However, the in vivo roles of these remain unknown. Gene expression assays showed that the transcripts of Me RAV s were commonly regulated after Xanthomonas axonopodis pv manihotis ( Xam ) and Me RAV s were specifically located in plant cell nuclei. Through virus‐induced gene silencing ( VIGS ) in cassava, we found that Me RAV 1 and Me RAV 2 are essential for plant disease resistance against cassava bacterial blight, as shown by the bacterial propagation of Xam in plant leaves. Through VIGS in cassava leaves and overexpression in cassava leave protoplasts, we found that Me RAV 1 and Me RAV 2 positively regulated melatonin biosynthesis genes and the endogenous melatonin level. Further investigation showed that Me RAV 1 and Me RAV 2 are direct transcriptional activators of 3 melatonin biosynthesis genes in cassava, as evidenced by chromatin immunoprecipitation‐ PCR in cassava leaf protoplasts and electrophoretic mobility shift assay. Moreover, cassava melatonin biosynthesis genes also positively regulated plant disease resistance. Taken together, this study identified Me RAV 1 and Me RAV 2 as common and upstream transcription factors of melatonin synthesis genes in cassava and revealed a model of Me RAV 1 and Me RAV 2 ‐melatonin biosynthesis genes‐melatonin level in plant disease resistance against cassava bacterial blight.