BpAP1 directly regulates BpDEF to promote male inflorescence formation in Betula platyphylla × B. pendula.

Flowering is a crucial process for plants that is under complex genetic control. AP1 acts as an organizer and a switch for the transition from vegetative to reproductive growth. In our previous study, we found that overexpression of BpAP1 significantly promoted the formation of male inflorescence in birch (Betula platyphlla × B. pendula). In this study, we aimed at investigating the molecular regulatory mechanism of BpAP1 during the process of male inflorescence formation in birch. We found that overexpression of BpAP1 affected the expression of many flowering-related genes, and had significant effect on B class MADS-box genes. A BpAP1-mediated gene regulatory network was constructed and B class gene BpDEF was finally predicted as a key target gene of BpAP1. Chromatin immunoprecipitation results indicated that BpAP1 could directly regulate BpDEF during the process of male inflorescence formation. Yeast one-hybrid assays and its validation in tobacco results suggested that BpAP1 regulated BpDEF via binding to a consensus DNA sequence known as CArG box. Gene function analysis of BpDEF indicated that BpDEF may function in sex-determination, and in particular specify the identity of male inflorescence in birch. Our results provide valuable clues for our understanding of the molecular mechanism of BpAP1 during the process of male inflorescence formation in birch.