Abstract

WRKY transcription factors are involved in plant defense against pathogens. No WRKYs have been reported to be involved in resistance to tobacco brown spot disease caused by Alternaria alternata. Here, we found that NaWRKY3 plays a critical role in Nicotiana attenuata defense against A. alternata. NaWRKY3 bound and regulated many defense genes, including: lipoxygenase 3, ACC synthase 1, and ACC oxidase 1, three jasmonate- and ethylene-biosynthetic genes; feruloyl-CoA 6ʹ-hydroxylase 1 (NaF6ʹH1), the biosynthetic gene for the phytoalexins scopoletin and scopolin; and three A. alternata resistance genes, the long non-coding RNA L2, NADPH oxidase (NaRboh D), and berberine bridge-like (NaBBL28). Silencing L2 reduced jasmonate concentrations and NaF6ʹH1 expression. NaRboh D-silenced plants were severely impaired in reactive oxygen species production and stomatal closure responses. NaBBL28 was the first A. alternata resistance BBL identified and was involved in the hydroxylation of 17-hydroxygeranyllinalool diterpene glycosides. NaWRKY3 bound to its own promoter but repressed its expression. Thus, we demonstrated that NaWRKY3 is a fine-tuned master regulator of the defense network against A. alternata in N. attenuata by regulating several signaling pathways and defense metabolites. This is the first time such an important WRKY has been identified in Nicotiana species, providing new insights into defense against A. alternata.