The role of α-globulin accumulation in seed storage protein reprogramming and grain quality in rice

Abstract The 26-kDa α-globulin, a minor component of rice seed storage proteins (SSPs), is encoded by the single-copy gene α-globulin 1 (Glb1), which is specifically expressed in the endosperm. However, the specific effects of altered α-globulin content on SSP composition and grain quality remains poorly understood. In this study, we demonstrated that modulation of α-globulin levels significantly enhances both total protein content and essential amino acid lysine accumulation in Glb1 knockout mutants and overexpression lines. Notably, specific alterations in SSP composition were observed exclusively in Glb1 mutants, with no such changes detected in overexpression lines. Glb1 knockout mutant produced abnormal protein bodies, including small-sized protein body I (PBI) and center-cracked PBII. Furthermore, increased proglutelin accumulation in Glb1 mutants triggered endoplasmic reticulum (ER) stress, resulting in a higher chalky grain rate. However, the altered α-globulin content had minimal effects on grain weight and starch properties compared to the wild type. This study elucidates the role of α-globulin accumulation in SSP reprogramming and provides a potential strategy for enhancing rice endosperm lysine content through the regulation of Glb1 biosynthesis.