The redistribution of protein sulfur in transgenic rice expressing a gene for a foreign, sulfur‐rich protein

Abstract

SummarySulfur amino acid composition is an important determinant of seed protein quality. A chimeric gene encoding sun¯ower seed albumin (SSA), one of the most sulfur-rich seed storage proteins identi®ed so far, was introduced into rice (Oryza sativa) in order to modify cysteine and methionine content of the seed. Analysis of a transgenic line expressing SSA at approximately 7% of total seed protein revealed that the mature grain showed little change in the total sulfur amino acid content compared to the parental genotype. This result indicated that the transgenic rice grain was unable to respond to the added demand for cysteine and methionine imposed by the production of SSA. Analysis of the protein composition of the transgenic grain showed changes in the relative levels of the major seed storage proteins, as well as some non-storage proteins, compared to non-transgenic controls. Changes observed at the protein level were concomitant with differences in mRNA accumulation but not always with the level of transcription. The limited sulfur reserves appeared to be re-allocated from endogenous proteins to the new sulfur sink in the transgenic grain. We hypothesize that this response is mediated by a signal transduction pathway that normally modulates seed storage protein composition in response to environmental¯uctuations in sulfur availability, via both transcriptional and post-transcriptional control of gene expression.

Gene-gene interactions between mutants that accumulate abnormally high amounts of proglutelin in rice seed

“…The accumulation of foreign protein within the ER induces an unfolded protein response resulting in the accumulation of the molecular chaperone BiP (Hagan et al 2003, Takemoto et al 2002, Yasuda et al 2006. In esp2 seeds, proglutelin accumulates in the ER accompanied by elevated BiP levels, reflecting an unfolded protein response (Satoh-Cruz et al 2010a).…”

Improving the Content of Essential Amino Acids in Crop Plants: Goals and Opportunities

“…Although a large array of sulfur-rich proteins have been tested (see the following reviews as examples: Muntz et al, 1998;Tabe and Higgins, 1998;Tabe and Droux, 2002;Hagan et al, 2003;Galili et al, 2005;Amir and Tabe, 2006), the most commonly used and most successful approaches in terms of increased Met content included expressing heterologous, natural Met-rich storage proteins, such as the 2S albumin from Brazil nut (Bertholletia excelsa) and sunflower (Helianthus annuus). Therefore, we will focus in this review on expression of these two proteins in seeds of transgenic plants.…”

“…Significant enhancement of total seed Met was observed in some of these plant species, and in some cases was still below the optimal level required for human food and animal feed (Altenbach et al, 1992;Saalbach et al, 1995;Molvig et al, 1997;Tabe and Higgins, 1998;Tabe and Droux, 2002;Hagan et al, 2003;Lee et al, 2003;Chiaiese et al, 2004;Amir and Tabe, 2006). This was largely because production of the proteins came at the expense of endogenous sulfur-rich compounds, such as free Met, Cys, and glutathione, as well as endogenous Met-rich proteins.…”

Silencing of Soybean Seed Storage Proteins Results in a Rebalanced Protein Composition Preserving Seed Protein Content without Major Collateral Changes in the Metabolome and Transcriptome

“…Legumes such as soybean possess storage proteins with low sulfur amino acid content. The b-subunit of conglycinin exhibits plasticity in response to available sulfur (Holowach et al, 1986;Hirai et al, 1995;Tabe et al, 2002;Hagan et al, 2003). There is also feedback regulation of protein filling in the seed sink in response to nitrogen availability (Biermann et al, 1998;Ohtake et al, 2002).…”