PDIL2-3 encoding a protein disulfide isomerase-like enzyme is essential for grain yield and appearance quality in rice (Oryza sativa L.)

Rice grain size and chalkiness are important traits that influence grain yield and quality, respectively. Mining of genes for grain yield and appearance quality and clarification of their action modes are of great importance in rice breeding. In this study, a rice protein disulfide isomerase-like enzyme PDIL2-3 was characterized. Expression analysis revealed that PDIL2-3 was highly expressed in endosperm and spikelet hulls. The PDIL2-3-cri lines generated by CRISPR/Cas9 technology exhibited a chalky grain phenotype with altered storage substance accumulation and increased grain size and weight, whereas exactly opposite results were obtained for PDIL2-3 overexpression lines. Cytological experiments revealed that PDIL2-3-cri increased rice seed length mainly by increasing the cell number and rice seed width mainly by increasing the cell size in grains, implying that PDIL2-3 regulates the grain size by influencing both cell division and expansion of spikelet hulls. Further flow cytometric analysis validated that PDIL2-3 has a negative effect on cell proliferation, preventing DNA duplication and cell division in spikelet hulls. Moreover, qRT-PCR results showed that the expression levels of genes related to cell cycle and storage substance synthesis were significantly changed in PDIL2-3-cri transgenic lines. Thus, our results indicated that PDIL2-3 plays a pivotal role in influencing grain size and quality of rice by affecting cell division/expansion and storage substance accumulation, providing new insights into the function of PDIL family members in rice and enriching the genetic resources for rice breeding.