AT-hook transcription factors restrict petiole elongation by inhibiting PIF-activated genes (Curr. Biol.)

The AT-hook motif nuclear localized (AHL) transcription factor family has one or two DNA-binding motifs to bind to AT rich DNA regions, and they also have a conserved PPC-DUF domain for protein-protein interactions. AHLs affect a wide range of biotic and abiotic responses but the mechanism of how they regulate transcription are still not well understood. Favero et al. report the first ChIP-seq analysis of an AHL family member, SOB3/AHL29, and show that AHL29 represses the transcription of PIF-regulated (Phytochrome-interacting factor) genes. Consistent with this finding, the sob3-6 mutant has increased petiole length while the pif4 mutant has the opposite phenotype, and the transcriptomes of AHL and PIF mutants show that AHL oppositely affects the transcription of large numbers PIF-regulated genes. Furthermore, ChIP-seq of AHL29 and PIF4/5 reveal that both proteins bind to similar regions in their target genes. Taken together, the authors conclude that AHLs repress petiole growth by decreasing PIF occupancy at growth-promoting genes through inhibiting the transcriptional activation.  (Summary by Min May Wong) Curr. Biol. 10.1016/j.cub.2020.02.017