LG1 promotes preligule band formation through directly activating ZmPIN1 genes in maize

Increasing plant density is an effective strategy for enhancing crop yield per unit land area. A key architectural trait for crops adapting to high planting density is a smaller leaf angle (LA). Previous studies have demonstrated that LG1, a SQUAMOSA BINDING PROTEIN (SBP) transcription factor, plays a critical role in LA establishment. However, the molecular mechanisms underlying the regulation of LG1 on LA formation remain largely unclear. In this study, we conduct comparative RNA-seq analysis of the preligule band (PLB) region of wild type and lg1 mutant leaves. Gene Ontology (GO) term enrichment analysis reveals enrichment of phytohormone pathways and transcription factors, including three auxin transporter genes ZmPIN1a, ZmPIN1b, and ZmPIN1c. Further molecular experiments demonstrate that LG1 can directly bind to the promoter region of these auxin transporter genes and activate their transcription. We also show that double and triple mutants of these ZmPINs genes exhibit varying degrees of auricle size reduction and thus decreased LA. On the contrary, overexpression of ZmPIN1a causes larger auricle and LA. Taken together, our findings establish a functional link between LG1 and auxin transport in regulating PLB formation and provide valuable targets for genetic improvement of LA for breeding high-density tolerant maize cultivars.