Transcriptional regulation by an NAC (NAM–ATAF1,2–CUC2) transcription factor attenuates ABA signalling for efficient basal defence towards Blumeria graminis f. sp.hordei in Arabidopsis

Abstract

Summary: ATAF1 is a member of a largely uncharacterized plant‐specific gene family encoding NAC transcription factors, and is induced in response to various abiotic and biotic stimuli in Arabidopsis thaliana. Previously, we showed that a mutant allele of ATAF1 compromises penetration resistance in Arabidopsis with respect to the non‐host biotrophic pathogen Blumeria graminis f. sp.hordei(Bgh). In this study, we have used genome‐wide transcript profiling to characterize signalling perturbations in ataf1 plants following Bgh inoculation. Comparative transcriptomic analyses identified an over‐representation of abscisic acid (ABA)‐responsive genes, including the ABA biosynthesis gene AAO3, which is significantly induced in ataf1 plants compared to wild‐type plants following inoculation with Bgh. Additionally, we show that Bgh inoculation results in decreased endogenous ABA levels in an ATAF1‐dependent manner, and that the ABA biosynthetic mutant aao3 showed increased penetration resistance to Bgh compared to wild‐type plants. Furthermore, we show that ataf1 plants show ABA‐hyposensitive phenotypes during seedling development and germination. Our data support a negative correlation between ABA levels and penetration resistance, and identify ATAF1 as a new stimuli‐dependent attenuator of ABA signalling for the mediation of efficient penetration resistance in Arabidopsis upon Bgh attack.