Extensin-like Protein OsPEX1 Modulates Grain Filling in Rice

Grain filling is a vital factor influencing both rice grain yield and quality, yet its underlying mechanisms remain poorly understood. In this study, we perform a functional analysis of the grain-filling defective mutant <i>pex1</i> in rice. <i>pex1</i> plants produce seeds that are floury, thick-branched, and exhibit a significantly slower grain-filling rate compared to the wild type. Further analysis reveals that the <i>pex1</i> mutants accumulated more starch in the pericarp but exhibited a defect in starch accumulation in the endosperm during grain filling, indicating an impaired transport of photosynthetic products from the pericarp to the endosperm. Cells within the nucellar projection in the <i>pex1</i> mutant appear irregular and loose loosely arranged, consistent with defective transfer of assimilates. Expression analysis reveals a downregulation of key grain-filling genes during the filling phase in the <i>pex1</i> mutant compared to the wild type, which correlates with the reduced grain-filling rate. Subcellular localization suggests that OsPEX1 is associated with the endoplasmic reticulum. Our findings demonstrate that <i>OsPEX1</i> plays a crucial role in grain filling.