大刍草稀有等位基因促进玉米密植高产

密植是提高作物单位面积产量、促进粮食增产的重要途径之一。叶夹角是影响玉米(Zea mays)密植的关键因子。中国农业大学田丰课题组最近克隆了2个调控玉米叶夹角的数量性状位点(QTL)——UPA1和UPA2, 揭示了这2个位点的功能基因(brd1和ZmRAVL1)通过油菜素内酯(BR)信号通路调控叶夹角。UPA2位于ZmRAVL1上游9.5 kb, 可与DRL1蛋白结合。另一个影响玉米叶夹角的蛋白LG1可以激活ZmRAVL1的表达; DRL1蛋白与LG1蛋白直接互作抑制LG1对ZmRAVL1的激活表达。玉米祖先种大刍草(teosinte)的UPA2位点序列与DRL1蛋白结合能力更强, 导致大刍草ZmRAVL1的表达受到更强的抑制, 下调表达的ZmRAVL1进一步使下游基因brd1的表达下调, 进而降低叶环区的内源BR水平, 导致叶夹角变小。将大刍草的UPA2等位基因导入到玉米中或对玉米中ZmRAVL1进行基因编辑, 在密植条件下均可显著提高玉米产量。上述发现为高产玉米品种的分子育种改良提供了重要理论基础和基因资源。

A Teosinte Rare Allele Increases Maize Plant Density and Yield

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.