Abstract
Grain weight and grain number are important crop yield determinants. DA1 and DAR1 are the ubiquitin receptors that function as the negative regulators of cell proliferation during development in Arabidopsis. An arginine to lysine mutant at amino acid site 358 could lead to the da1-1 phenotype, which results in an increased organ size and larger seeds. In this study, the mutated ZmDA1 (Zmda1) and mutated ZmDAR1 (Zmdar1) driven by the maize ubiquitin promoter were separately introduced into maize elite inbred line DH4866. The grain yield of the transgenic plants was 15% greater than that of the wild-type in 3 years of field trials due to improvements in the grain number, weight and starch content. Interestingly, the over-expression of Zmda1 and Zmdar1 promoted kernel development, resulting in a more developed basal endosperm transfer cell layer (BETL) than WT and enhanced expression of starch synthase genes. This study suggests that the over-expression of the mutated ZmDA1 or ZmDAR1 genes improves the sugar imports into the sink organ and starch synthesis in maize kernels.