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Proteomics and Post-Translational Modifications of Starch Biosynthesis-Related Proteins in Developing Seeds of Rice.

ABSTRACT: Rice (Oryza sativa L.) is a foremost staple food for approximately half the world's population. The components of rice starch, amylose, and amylopectin are synthesized by a series of enzymes, which are responsible for rice starch properties and functionality, and then affect rice cooking and eating quality. Recently, proteomics technology has been applied to the establishment of the differentially expressed starch biosynthesis-related proteins and the identification of posttranslational modifications (PTMs) target starch biosynthesis proteins as well. It is necessary to summarize the recent studies in proteomics and PTMs in rice endosperm to deepen our understanding of starch biosynthesis protein expression and regulation, which will provide useful information to rice breeding programs and industrial starch applications. The review provides a comprehensive summary of proteins and PTMs involved in starch biosynthesis based on proteomic studies of rice developing seeds. Starch biosynthesis proteins in rice seeds were differentially expressed in the developing seeds at different developmental stages. All the proteins involving in starch biosynthesis were identified using proteomics methods. Most starch biosynthesis-related proteins are basically increased at 6-20 days after flowering (DAF) and decreased upon the high-temperature conditions. A total of 10, 14, 2, 17, and 7 starch biosynthesis related proteins were identified to be targeted by phosphorylation, lysine acetylation, succinylation, lysine 2-hydroxyisobutyrylation, and malonylation, respectively. The phosphoglucomutase is commonly targeted by five PTMs types. Research on the function of phosphorylation in multiple enzyme complex formation in endosperm starch biosynthesis is underway, while the functions of other PTMs in starch biosynthesis are necessary to be conducted in the near future.

SUBMITTER: Tappiban P

PROVIDER: S-EPMC8199009 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Starch is the major component of cereal grains and is composed of essentially linear amylose and highly branched amylopectin. The properties and composition of starch determine the use and value of grains and their products. Starch synthase (SS) I, SSIIa, and SSIIIa play central roles in amylopectin biosynthesis. These three SS isozymes also affect seed development, as complete loss of both SSI and SSIIIa under reduced SSIIa activity in rice lead to sterility, whereas presence of minimal SSI or SSIIIa activity is sufficient for generating fertile seeds. SSs, branching enzymes, and/or debranching enzymes form protein complexes in cereal. However, the relationship between starch properties and the formation of protein complexes remain largely unknown. To better understand this phenomenon, properties of starch and protein complex formation were analyzed using developing mutant rice seeds (ss1 L /ss2a L /ss3a) in which all three major SS activities were reduced.The SS activity of ss1 L /ss2a L /ss3a was 25%-30% that of the wild-type. However, the grain weight of ss1 L /ss2a L /ss3a was 89% of the wild-type, 55% of which was starch, showing considerable starch synthesis. The reduction of soluble SS activity in ss1 L /ss2a L /ss3a resulted in increased levels of ADP-glucose pyrophosphorylase and granule-bound starch synthase I, which are responsible for substrate synthesis and amylose synthesis, respectively. Together, these features led to an increase in apparent amylose content (34%) in ss1 L /ss2a L /ss3a compared with wild-type (20%). Gel filtration chromatography of the soluble proteins in ss1 L /ss2a L /ss3a showed that the majority of the starch biosynthetic enzymes maintained the similar elution patterns as wild-type, except that the amounts of high-molecular-weight SSI (>?300 kDa) were reduced and SSIIa of approximately 200-300 kDa were present instead of those >?440 kDa, which predominate in wild-type. Immuno-precipitation analyses suggested that the interaction between the starch biosynthetic enzymes maybe reduced or weaker than in wild-type.Although major SS isozymes were simultaneously reduced in ss1 L /ss2a L /ss3a rice, active protein complexes were formed with a slightly altered pattern, suggesting that the assembly of protein complexes may be complemented among the SS isozymes. In addition, ss1 L /ss2a L /ss3a maintained the ability to synthesize starch and accumulated less amylopectin and more amylose in starch.

Project description:Lysine succinylation has been recognized as a post-translational modification (PTM) in recent years. It is plausible that succinylation may have a vaster functional impact than acetylation because of bulkier structural changes and more significant charge differences on the modified lysine residue. Currently, however, the quantity and identity of succinylated proteins and their corresponding functions in cereal plants remain largely unknown. In this study, we estimated the native succinylation occupancy on lysine was between 2% to 10% in developing rice seeds. Eight hundred fifty-four lysine succinylation sites on 347 proteins have been identified by a thorough investigation in developing rice seeds. Six motifs were revealed as preferred amino acid sequence arrangements for succinylation sites, and a noteworthy motif preference was identified in proteins associated with different biological processes, molecular functions, pathways, and domains. Remarkably, heavy succinylation was detected on major seed storage proteins, in conjunction with critical enzymes involved in central carbon metabolism and starch biosynthetic pathways for rice seed development. Meanwhile, our results showed that the modification pattern of in vitro nonenzymatically succinylated proteins was different from those of the proteins isolated from cells in Western blots, suggesting that succinylation is not generated via nonenzymatic reaction in the cells, at least not completely. Using the acylation data obtained from the same rice tissue, we mapped many sites harboring lysine succinylation, acetylation, malonylation, crotonylation, and 2-hydroxisobutyrylation in rice seed proteins. A striking number of proteins with multiple modifications were shown to be involved in critical metabolic events. Given that these modification moieties are intermediate products of multiple cellular metabolic pathways, these targeted lysine residues may mediate the crosstalk between different metabolic pathways via modifications by different moieties. Our study exhibits a platform for extensive investigation of molecular networks administrating cereal seed development and metabolism via PTMs.

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Proteomics and Post-Translational Modifications of Starch Biosynthesis-Related Proteins in Developing Seeds of Rice.

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