Hbi1 Acts Downstream Of Erecta And Swr1 In Regulating Inflorescence Architecture Through The Activation Of The Brassinosteroid And Auxin Signaling Pathways

Inflorescence architecture critically influences plant reproductive success and crop yield, and it reflects the activity of the inflorescence meristem and pedicel length. InArabidopsis thaliana, the ERECTA (ER) signaling pathway and the SWR1 chromatin remodeling complex jointly regulate inflorescence architecture by promoting the expression of thePACLOBUTRAZOL RESISTANCE(PRE) gene family. However, howPREs regulate inflorescence architecture remains unclear. RNA-sequencing and chromatin immunoprecipitation coupled with quantitative PCR analyses were performed. Genetic interactions betweenHOMOLOG OF BEE2 INTERACTING WITH IBH1(HBI1) and the SWR1-ER-MPK6 pathway in the control of inflorescence architecture were further studied. The present findings support thatHBI1functions downstream ofPREs in the SWR1 and ER pathways to regulate inflorescence architecture by promoting pedicel elongation. Specifically, it binds to the promoters of the brassinosteroid (BR) biosynthesis geneCYP85A2and a series of auxin-related genes, including auxin response factorARF3, and promotes their expression. In turn, ARF3 can also bind to auxin signaling genes as well asCYP85A2to activate their expression and promote pedicel elongation. Our study provides evidence that inflorescence architecture regulation by SWR1 and ER involves the HBI1 regulatory hub and its activation of both the BR and auxin hormone pathways.