ZmTCP23 regulates leaf angle and tassel branch angle formation in maize by modulating LG1 expression and abscisic acid catabolism.

Leaf angle (LA) and tassel branch angle (TBA) are two important agronomic traits influencing maize plant architecture, thereby affecting its adaptability to high-density planting. Liguleless1 (LG1) acts as a key regulator of LA and TBA, yet its precise regulatory mechanism remains largely obscure. In this study, we have identified ZmTCP23, a teosinte branched1/CYCLOIDEA/proliferating cell factors (TCP) transcription factor that is highly expressed in tassel and leaf primordia, serving as a pivotal upstream transcriptional regulator of LG1. The functional loss of ZmTCP23 results in a significant reduction in both TBA and LA ranges. Moreover, in vitro and in vivo studies revealed that LG1 directly represses the expression of ZmXERICO1, a gene encoding an inhibitor of abscisic acid (ABA) degradation that can also influence LA and TBA upon overexpression. Additionally, ZmTCP23 physically interacts with the previously identified TBA regulator BAD1, forming a complex that co-activates the expression of LG1 via direct binding to its promoter. This dynamic duo established a positive feedback loop, mutually enhancing each other's expression within the tassels, and consequently influencing TBA. Our findings establish a ZmTCP23-LG1-ZmXERICO1 transcriptional regulatory cascade that orchestrates LA and TBA through influencing ABA content, and provide new targets for the genetic manipulation of LA and TBA for molecular breeding of high-density tolerant maize cultivars.