Regulation of ARGONAUTE10 Expression Enables Temporal and Spatial Precision in Axillary Meristem Initiation in Arabidopsis

Axillary meristems (AMs) give rise to lateral shoots and are critical to plant architecture. Understanding how developmental cues and environmental signals impact AM development will enable the improvement of plant architecture in agriculture. Here, we show that ARGONAUTE10 (AG010), which sequesters miR165/166, promotes AM development through the miR165/166 target gene REVOLUTA. We reveal that AG010 expression is precisely controlled temporally and spatially by auxin, brassinosteroids, and light to result in AM initiation only in the axils of leaves at a certain age. AUXIN RESPONSE FACTOR 5 (ARF5) activates while BRASSINAZOLE-RESISTANT 1 (BZR1) and PHYTOCHROME-INTERACTING FACTOR 4 (PIF4) repress AG010 transcription directly. In axils of young leaves, BZR1 and PIF4 repress AG010 expression to prevent AM initiation. In axils of older leaves, ARF5 upregulates AG010 expression to promote AM initiation. Our results uncover the spatiotemporal control of AM development through the cooperation of hormones and light converging on a regulator of microRNA.