Vacuolar Processing Enzyme plays an Essential Role in the Crystalline Structure of Glutelin in Rice Seed

Abstract

To identify the function of genes that regulate the processing of proglutelin, we performed an analysis of glup3 mutants, which accumulates excess amounts of proglutelin and lack the vacuolar processing enzyme (VPE). VPE activity in developing seeds from glup3 lines was reduced remarkably compared with the wild type. DNA sequencing of the VPE gene in glup3 mutants revealed either amino acid substitutions or the appearance of a stop codon within the coding region. Microscopic observations showed that alpha-globulin and proglutelin were distributed homogeneously within glup3 protein storage vacuoles (PSVs), and that glup3 PSVs lacked the crystalline lattice structure typical of wild-type PSVs. This suggests that the processing of proglutelin by VPE in rice is essential for proper PSV structure and compartmentalization of storage proteins. Growth retardation in glup3 seedlings was also observed, indicating that the processing of proglutelin influences early seedling development. These findings indicate that storage of glutelin in its mature form as a crystalline structure in PSVs is required for the rapid use of glutelin as a source of amino acids during early seedling development. In conclusion, VPE plays an important role in the formation of protein crystalline structures in PSVs.

Dynamic Proteomics Emphasizes the Importance of Selective mRNA Translation and Protein Turnover during Arabidopsis Seed Germination

“…This result highlights that the vacuolar-processing enzyme involved in post-translational processing of the precursor cruciferin forms into the corresponding acid and basic 12S cruciferin subunits is functional during the very early steps of seed germination. Vacuolar-processing enzyme is essential for the correct protein storage vacuole structure and compartmentalization of SSPs, and a seedling growth delay was reported in rice vpe mutants (48,49). This indicates that SSP processing can affect early seedling development, presumably because such processing is required for the rapid use of these proteins as a source of nitrogen and amino acids.…”

Delivery of Prolamins to the Protein Storage Vacuole in Maize Aleurone Cells

“…When protein inclusions inside PSVs appear as a crystalline lattice, they are called crystalloids. Crystalloids have been described in rice and in seeds of some dicots, such as tomato (Solanum lycopersicum) and pumpkin (Cucurbita maxima; Krishnan et al, 1986;Krishnan and White, 1995;Kumamaru et al, 2010). Besides storage proteins, crystalloids contain integral membrane proteins and lipids, which have been hypothesized to form a multilamellar membrane/lattice structure (Jiang et al, 2000;Gillespie et al, 2005;Oufattole et al, 2005).…”

Ultrastructure of protein bodies in mutant rice (Oryza sativa L.) with altered storage protein composition

“…Glutelin and globulin are components of PB-II (Yamagata et al 1982), but the influence of their reduction on PB structure was different. Studies on protein-sorting mutants revealed that deficiency of protein disulfide isomerase or vacuolar processing enzyme affects PB structure (Kumamaru et al 2010, Takemoto et al 2002, Wang et al 2009). The present study showed that storage protein itself plays an important role in formation of normal PB.…”

“…The glutelin precursor mutant 3 (glup3) mutant, which also accumulates high content of 57 kDa proglutelin polypeptides and low content of the glutelin acidic and basic subunits, shows normal PB-I in appearance and round-shaped PB-II. The round-shaped PB-II doesn't show crystalline structure typical of wild-type PB-II (Kumamaru et al 2010). These mutants with altered storage protein composition arise from mutation in protein-sorting genes; the esp2 mutant is deficient in protein disulfide isomerase, and the Glup3 gene encodes vacuolar processing enzyme (Kumamaru et al 2010, Takemoto et al 2002.…”