An AT-hook motif nuclear protein AHL13 interacts with Poly(ADP-ribose) to regulate Arabidopsis immunity

Poly(ADP-ribosyl)ation or PARylation is required for immune transcription and defense against microbes in plants. However, the mechanisms underlying the PARylation-mediated transcriptional regulation are largely unknown. In this study, an AT-hook motif nuclear localized transcription factor, AHL13, was identified as an interactor of poly (ADP-ribose), the polymer products of PARylation. The knock-out and over-expression experiments suggest that AHL13 functions as a negative regulator of Arabidopsis immunity. RNA seq results showed that a group of defense-related genes were repressed by AHL13 upon bacterial infection. AHL13 could directly bind to the AT-rich sequences in the promoters of the target genes in the EMSA and MST assays. The PAR polymers directly interact with AHL13 with high affinity and significantly suppress its interaction with the AT-rich DNA, suggesting that PARylation might promote immune transcription through a repressor-repelling mechanism. In summary, this study revealed that the PAR-AHL13 interaction plays significant roles in immune gene expression in Arabidopsis.