Abstract
The major seed storage proteins (SSPs) in rice seeds have been classified into three types, glutelins, prolamins, and globulin, and the proportion of each SSP varies. It has been shown in rice mutants that when either glutelins or prolamins are defective, the expression of another type of SSP is promoted to counterbalance the deficit. However, we observed reduced abundances of glutelins and prolamins in dry seeds of a globulin-deficient rice mutant (Glb-RNAi), which was generated with RNA interference (RNAi)-induced suppression of globulin expression. The expression of the prolamin and glutelin subfamily genes was reduced in the immature seeds of Glb-RNAi lines compared with those in wild type. A proteomic analysis of Glb-RNAi seeds showed that the reductions in glutelin and prolamin were conserved at the protein level. The decreased pattern in glutelin was also significant in the presence of a reductant, suggesting that the polymerization of the glutelin proteins via intramolecular disulfide bonds could be interrupted in Glb-RNAi seeds. We also observed aberrant and loosely packed structures in the storage organelles of Glb-RNAi seeds, which may be attributable to the reductions in SSPs. In this study, we evaluated the role of rice globulin in seed development, showing that a deficiency in globulin could comprehensively reduce the expression of other SSPs.
Highlights
Storage proteins constitute up to ~12% of the seed dry weight in cereal plants and these proteins are predominantly founded in the aleurone and subaleurone layers of the seed endosperm [1]
The signal recognized by an anti-globulin antibody was clearly observed in wild-type protein extract but was undetectable in the protein extracts from the Glb-RNA interference (RNAi) plants (Figure 1a, right panel)
The total seed proteins were isolated from both wild type and transformants, and separated into three fractions containing prolamin, globulin, and glutelin, according to their differential solvent solubilities: the glutelins in rice seeds are soluble in alkali solution [2], the prolamins are soluble in alcohol [33], and the globulin proteins are soluble in saline solution [34]
Summary
Storage proteins constitute up to ~12% of the seed dry weight in cereal plants and these proteins are predominantly founded in the aleurone and subaleurone layers of the seed endosperm [1]. The first type of mutants arises from the direct disruption of endogenous SSP gene expression [24,25,26] Some rice mutants, such as glu, glu, and glu, are characterized by the deletion of glutelin family spots from two-dimensional electrophoresis (2-DE) gels [27]. Previous SSP studies have characterized the molecular localization of storage proteins and the formation of the storage organelles in rice seeds These studies have investigated various aspects of cellular processes, including protein synthesis, intracellular transport mechanisms, and endosperm development. Studies of mutants with defects in seed-specific storage proteins have suggested that there are different molecular requirements for the accumulation of SSPs under different conditions, altering the expression of storage protein gene families and the differentiation of storage organelles, generating different seed phenotypes. The results extend our understanding of the regulation of SSP accumulation and the comprehensive packaging of SSPs during seed development
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