Class II diacylglycerol kinases participate in the basal immune responses of Nicotiana benthamiana to Ralstonia solanacearum

Abstract

Phospholipid signaling plays an important role in Nicotiana benthamiana immune responses to phytopathogenic bacteria. In this study, we isolated three orthologs encoding class II diacylglycerol kinase (NbDGK4-1, NbDGK4-2 and NbDGK7) in the N. benthamiana genome. In contrast to the undetectable expression of NbDGK4-2, the NbDGK4-1 and NbDGK7 expression levels increased in response to Ralstonia solanacearum and the flg22 peptide. The induction of the hypersensitive response was not affected, but bacterial growth increased and the onset of bacterial wilt symptoms was accelerated in the NbDGK4-1-silenced and NbDGK7-silenced plants challenged with R. solanacearum. The expression levels of NbPR-1 and NbPR-4 (marker genes for salicylic acid and jasmonic acid signaling, respectively) decreased in the NbDGK4-1-silenced and NbDGK7-silenced plants inoculated with R. solanacearum. The expression of pathogen-associated molecular pattern-triggered immunity (PTI) marker genes were also inhibited in the NbDGK4-1-silenced and NbDGK7-silenced plants infiltrated with the type III secretion system (T3SS)-deficient R. solanacearum mutant or flg22. Accordingly, the T3SS-deficient R. solanacearum bacterial population increased in the NbDGK4-1-silenced and NbDGK7-silenced plants. Moreover, flg22-induced resistance and callose deposition were also compromised in the NbDGK4-1-silenced and NbDGK7-silenced plants. Considered together, the study results indicate class II diacylglycerol kinases may be important for N. benthamiana basal disease resistance (e.g., PTI responses).