GSE122455
AT-hook transcription factors repress petiole growth by antagonizing PIF4 [ChIP-seq]
As sessile organisms, plants rely heavily on growth and developmental plasticity to respond to external challenges threatening their survival. Strict regulation of growth in organs such as hypocotyls and petioles enables plants to respond optimally to varying environmental conditions, such as changes in light and temperature, while also ensuring that resources are not needlessly wasted on unnecessary growth. Studies performed in Arabidopsis thaliana have established the PHYTOCHROME INTERACTING FACTOR (PIF) transcription factor family as key positive regulators of growth, particularly in hypocotyls and petioles. In this study, we identify members of the AT-HOOK MOTIF NUCLEAR LOCALIZED (AHL) family, including SUPPRESSOR OF PHYTOCHROME B4-#3 (SOB3), as repressors of PIF4-mediated petiole elongation. Specifically, we found that high levels of SOB3 lead to a short-petiole phenotype similar to that conferred by removal of PIF4. Conversely, the dominant-negative sob3-6 mutant has long petioles, a phenotype which is dependent on PIF4. Additionally, we show that AHLs repress the expression of many PIF-activated genes, including a number involved in hormone-mediated promotion of growth and a subset of which are directly bound by both SOB3 and PIFs. Taken together these results suggest that AHLs repress petiole growth by antagonizing PIF-mediated transcriptional activation of growth-promoting genes, including ARABIDOPSIS THALIANA HOMEOBOX PROTEIN 2 (ATHB2), BRASSINOSTEROID INSENSITIVE 1 (BRI1), INDOLE-3-ACETIC ACID INDUCIBLE 19 (IAA19), PIN-FORMED 3 (PIN3), SMALL AUXIN UP RNA 24 (SAUR24), and YUCCA8 (YUC8). Elucidating a mechanism by which positive and negative growth factors influence growth in petioles achieves a critical first step towards understanding the gene regulatory networks which modulate leaf growth in response to the environment. Overall design: Genome-wide identification of SOB3 binding sites in juvenile rosettes of Arabidopsis