WRKY22 and WRKY25 transcription factors are positive regulators of defense responses inNicotiana benthamiana

Key message NbWRKY22 and NbWRKY25 are required for full activation of bacteria-associated pattern- and effector-triggered immunity as well as for the response to other non-bacterial defense elicitors. Plants defend themselves against pathogens using a two-layered immune system. Pattern-triggered immunity (PTI) can be activated upon recognition of epitopes from flagellin including flg22.Pseudomonas syringaepv.tomato(Pst) delivers effector proteins into the plant cell to promote host susceptibility. However, some plants express resistance (R) proteins that recognize specific effectors leading to the activation of effector-triggered immunity (ETI). Resistant tomato lines such as Rio Grande-PtoR (RG-PtoR) recognize twoPsteffectors, AvrPto and AvrPtoB, and activate ETI through the Pto/Prf protein complex. Using RNA-seq, we identified two tomato WRKY transcription factor genes,SlWRKY22andSlWRKY25, whose expression is increased duringPst-induced ETI. Silencing of theWRKY25/22orthologous genes inNicotiana benthamianaled to a delay in programmed cell death normally associated with AvrPto recognition or several non-bacterial effector/R protein pairs. An increase in disease symptoms was observed in silenced plants infiltrated withPseudomonas syringaepv. tabaciexpressing AvrPto or HopQ1-1. Expression of both tomatoWRKYgenes is also induced upon treatment with flg22 and callose deposition and cell death suppression assays inWRKY25/22-silencedN. benthamianaplants supported their involvement in PTI. Our results reveal an important role for two WRKYs as positive regulators of plant immunity against bacterial and potentially non-bacterial pathogens.