Abstract: 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.

Key words: ABA, leaf angle, LG1, maize, tassel branch angle, ZmTCP23