Abstract: Increasing plant density is an important approach to boost crop yield, and leaf angle is one of the key factors affecting plant density. Recently, Feng Tian’s lab from China Agricultural University cloned and characterized two major QTLs (UPA1 and UPA2) regulating leaf angle in maize. The underlying genes are brd1 and ZmRAVL1, respectively, and both of them are involved in the brassinosteroid (BR) pathway to regulate leaf angle. UPA2 is located 9.5 kb upstream of ZmRAVL1 and is bound by DRL1. LG1, another leaf angle protein, directly activates the expression of ZmRAVL1. DRL1 and LG1 physically interact and the resulting complex in turn represses the LG1-activated expression of ZmRAVL1. The teosinte allele of UPA2 has a higher binding affinity with DRL1, resulting in the reduced ZmRAVL1 expression, which consequently down-regulates the brd1 expression and leads to the decreased brassinosteroid level, thereby reducing the leaf angle. The introgression of UPA2 teosinte allele into maize and the manipulation of ZmRAVL1 significantly increase maize yield with increased plant density. These findings have paved a new avenue for molecular breeding of high-yield maize varieties.

Key words: maize, plant density, yield, UPA1, UPA2