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

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 accumulation of the essential amino acid lysine 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 mutants produced abnormal protein bodies, including small-sized protein body I and center-cracked protein body II. Furthermore, increased proglutelin accumulation in Glb1 mutants triggered endoplasmic reticulum stress, resulting in a higher chalky grain rate. However, the altered α-globulin content had minimal effects on grain weight and starch properties compared with 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.