Endosperm-specific overexpression of Opaque2 improves maize kernel texture

Abstract

Kernel texture is a crucial agronomic trait that determines crop yield and nutrient quality, yet limited genes with breeding potentials have been identified for texture improvement. In maize, the endosperm-filling central regulator Opaque2 coordinately regulates starch and protein synthesis and plays pivotal roles in vitreous endosperm formation. In this study, we specifically overexpressed Opaque2 in the developing endosperm driven by the 27-kD γ zein promoter to investigate the effects on kernel texture, yield and nutrient quality. Notably, overexpression of Opaque2 enhanced test weight and 100-kernel weight despite reduced kernel dimensions. The overexpressed kernels exhibited improved kernel texture with expanded vitreous endosperm regions. Furthermore, the starch contents were increased, including elevated levels of amylose and amylopectin. The starch granules in the overexpressed endosperms were denser and more tightly packed. Zein accumulation was dramatically elevated in the overexpressed kernels in comparison with wild type, whereas nonzein levels were slightly decreased, resulting in elevated total protein synthesis. Further transcriptomic analysis comprehensively revealed that the Opaque2 overexpression positively influences a series of biological processes to precisely modulate vitreous endosperm formation and texture improvement. This work provides a novel insight into maize texture improvement through endosperm-specific overexpression of Opaque2.