miR394 and LCR cooperate with TPL to regulate AM initiation

The plant architecture is a main determinate of crop yield, and lateral branching significantly influences the number of inflorescences and seeds. Axillary buds support lateral branch growth, and the development of axillary buds includes two stages, initiation and outgrowth. Extensive studies on the outgrowth stage have uncovered fine regulatory mechanisms of branch growth, while our understanding of axillary bud initiation remains unclear. This work aims to study how miRNA regulate axillary bud initiation. By constructing small RNA library and screening mutant population, we identified miR394s promote axillary bud initiation. We found that the initiation of axillary buds is specifically induced by miR394 and repressed by its target LEAF CURLING RESPONSIVENESS (LCR) in the center of leaf axils. Using promoter-driven fluorescent tags and in situ hybridization, we showed that miR394 localized in the position where AMs initiate. Through molecular and genetic research, we found miR394 may regulate REVOLUTA-STM pathway to establish axillary meristem. Immunoprecipitation and mass spectrometry studies showed that LCR, as an F-box protein, interacted with TOPLESS (TPL) proteins and participate in ubiquitinated protein degradation. Our results reveal an important mechanism that miR394s regulated LCR accelerates the degradation of TPL to precisely modulate axillary bud initiation.