Submitted to: Frontiers in Plant Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/7/2014
Publication Date: N/A
Citation: Interpretive Summary: Sugars, including hexoses such as glucose and fructose, are major metabolic fuels in developing seeds in plants. Additionally, they perform many signaling functions through their role in modifications or decorations of many proteins known as glycoproteins (GPs). A large proportion of total proteins in all organisms are comprised of GPs that perform many critical function in development, including seed development in plants. However, nothing is known on the overall distribution and role of GPs in seed development. This report, based on cooperative investigations between scientists from CMAVE, SAA, USDA ARS and the University of Florida, Gainesville, FL, is aimed to provide a high-throughput profile of the total GPs in a normal and a hexose-deficient mutant seeds to both (a) catalogue and (b) to identify specific GPs potentially affected in the mutant genotype. The results show that many GPs in the mutant as compared to the normal were reduced in their levels of sugars attached to the proteins (i.e., under-glycosylated). Nearly all such proteins were also reduced in their absolute levels indicating that their stability was affected due to the under-glycosylation. Functional classification based on various bioinformatics tools showed many of these GPs perform a range of diverse cellular and metabolic functions during seed development. Future studies will be focused on certain specific proteins and genes for manipulation and, ultimately, to attain seed improvement.
Technical Abstract: Developing seeds of many plants have transfer cells. In maize, these are prominently located at the basal end of endosperm (a.k.a., basal endosperm transfer layer, BETL) and they are readily identifiable due to their unique morphology of long and dome-shaped cells filled with labyrinth-like wall-in-growth (WIG) because of secondary cell wall growth. As the first filial cell layer, BETL is a gateway to sugars, nutrients and water from mother plant, and also anchor numerous functions essential to normal seed development. Important functions include sucrose turnover, auxin and cytokinin biosynthesis\accumulation, energy metabolism, defense response, and signaling between maternal and filial generations. Our previous studies have shown that basal part of developing endosperm of miniature1 (mn1) seed mutant lacking the Mn1-encoded cell wall invertase, INCW2, are also deficient for hexose sugars, WIGs and Golgi as compared to the Mn1 seeds. Given the central role of Golgi as a primary site for protein glycosylation, and hexose as the main sugar in covalent modifications of various proteins, we performed a large scale glycoproteome profiling of total proteins in these two genotypes using two dimensional (2D) gel electrophoresis and protein staining for glycosylated and total protein, followed by image analysis. Protein identification was done by Liquid Chromatography Tandem MS (LC-MS/MS). We identified a total of 413 proteins and selected 254 differential proteins for further analysis. Of these, 113 proteins that matched between the two genotypes, 45 showed > 20% increase or decrease in their levels of glycosylation. A large number of the proteins showed decreased levels of glycosylation in mn1 developing endosperms as compared to the Mn1.