Arabidopsis downy mildew effector HaRxLL470 suppresses plant immunity by attenuating the DNA‐binding activity of bZIP transcription factor HY5

Abstract

The oomycete pathogen Hyaloperonospora arabidopsidis (Hpa) delivers diverse effector proteins into host plant cells to suppress plant innate immunity. In this study, we investigate the mechanism of action of a conserved RxLR effector HaRxLL470 in suppressing plant immunity. Genomic, molecular and biochemical analyses were performed to investigate the function of HaRxLL470 and the mechanism of the interaction between HaRxLL470 and the target host protein during Hpa infection. We report that HaRxLL470 enhances plant susceptibility to Hpa isolate Noco2 by interacting with the host photomorphogenesis regulator protein HY5. Our results demonstrate that HY5 is not only an important component in the regulation of light signalling, but also positively regulates host plant immunity against Hpa by transcriptional activation of defense‐related genes. We show that the interaction between HaRxLL470 and HY5 compromises the function of HY5 as a transcription factor by attenuating its DNA‐binding activity. The present study demonstrates that HY5 positively regulates host plant defense against Hpa whereas HaRxLL470, a conserved RxLR effector across oomycete pathogens, enhances pathogenicity by interacting with HY5 and suppressing transcriptional activation of defense‐related genes.