OsPEX1, a leucine-rich repeat extensin protein, functions in the regulation of caryopsis development and quality in rice

Rice caryopses are enclosed by outer glumes. The size and dimension of the outer glume are the main determinants of caryopsis size. However, it is unclear whether caryopsis development is completely dependent on the size of the glume, or whether it can grow and expand autonomously despite the con-straint of glume enclosure. We report the identification of a mutant line that produces normal-sized glumes with smaller mature caryopses that do not fill the entire glume cavity. The caryopsis phenotype in the pex1 mutant is caused by a reduction in cell size. OsPEX1, a leucine-rich repeat extensin gene, was highly expressed in the developing caryopsis. Overexpression of OsPEX1 driven by a constitutive pro-moter recapitulated the mutant phenotype, showing that the small-caryopsis phenotype is caused by overexpression of the OsPEX1 gene. Free amino acids, including several essential amino acids, and crude protein were increased in pex1 relative to the wild type, endowing pex1 with improved nutritional qual-ity. Our results suggest that caryopsis development can be genetically uncoupled from maternally con-trolled glume development and that OsPEX1 might be a new resource for improving nutritional quality of rice cultivars.(c) 2021 Crop Science Society of China and Institute of Crop Science, CAAS. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC -ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).