Proteome evolution of wheat (Triticum aestivum L.) aleurone layer at fifteen stages of grain development.

The aleurone layer (AL) is the grain peripheral tissue; it is rich in micronutrients, vitamins, antioxidants, and essential amino acids. This highly nutritive part of the grain has been less studied partly because its isolation is so laborious. In the present study, the ALs of Triticum aestivum (variety Récital) were separated manually at 15 stages of grain development. A total of 327 proteins were identified using 2-DE LC-MS/MS. They were classified in six main groups and 26 sub-groups according to their biochemical function. Proteomic analysis revealed seven different profiles distributed among three main development stages: (i) early AL development, with proteins involved in intense metabolic activities in the growth and development of the cell wall compounds; (ii) the intermediate stage, characterized by oxidative stress and defense proteins (65%) linked with loss of water in peripheral layers during grain filling; and (iii) AL maturation, involving the production of amino acids and the control of reactive oxidative species to enable the accumulation and maturation of globulins within the AL. The present study provides the first insights into developing proteome in the AL. We describe the numerous AL enzymes involved in the accumulation of storage protein and in the protection of the endosperm over time. BIOLOGICAL SIGNIFICANCE: The hand dissection of wheat aleurone layer (AL) was carried in this study for the first time on fifteen developmental stages from cell differentiation to grain maturity. Three major phases were revealed over AL development: cell division activities, globulins storage, and grain protection. Enzymes related to metabolites and vitamins were abundantly expressed during the two first phases. In parallel to the progressive globulins accumulation, the final phase was characterized by key enzyme synthesis involved in energy production, amino-acids and antioxidant synthesis plus others to face hypoxia and dehydration of grain tissues.

Expression profiling of starchy endosperm metabolic proteins at 21 stages of wheat grain development.

Proteomic analysis of albumins and globulins (alg) present in starchy endosperm of wheat (Triticum aestivum cv Récital), at 21 stages of grain development, led to the identification of 487 proteins. Four main developmental phases of these metabolic proteins, with three subphases in phase three and two in phase four, were shown. Hierarchical cluster analysis revealed nine major expression profiles throughout grain development. Classification of identified proteins in 17 different biochemical functions provided a uniform picture of temporal coordination among cellular processes. Proteins involved in cell division, transcription/translation, ATP interconversion, protein synthesis, protein transport, along with amino acid, lipid, carbohydrate and nucleotide metabolisms were highly expressed in early and early mid stages of development. Protein folding, cytoskeleton, and storage proteins peaked during the middle of grain development, while in later stages stress/defense, folic acid metabolism, and protein turn over were the abundant functional categories. Detailed analysis of stress/defense enzymes revealed three different evolutionary profiles. A global map with their predicted subcellular localizations and placement in grain developmental scale was constructed. The present study of complete grain development enriched our knowledge on proteome expression of alg, successively from endosperm cell division and differentiation to programmed cell death.

Proteomic analysis of peripheral layers during wheat (Triticum aestivum L.) grain development.

Grains of hexaploid wheat, Triticum aestivum (cv. Récital), were collected at 15 stages of development, from anthesis to physiological maturity, 0-700°C days (degree days after anthesis). Two hundred and seven proteins of grain peripheral layers (inner pericarp, hyaline, testa and aleurone layer) were identified by 2-DE, MALDI-TOF MS and data mining, then were classified in 16 different functional categories. Study of the protein expression over time allowed identification of five main profiles and four distinct phases of development. Composite expression curves indicated that there was a shift from metabolic processes, translation, transcription and ATP interconversion towards storage and defence processes. Protein synthesis, protein turnover, signal transduction, membrane transport and biosynthesis of secondary metabolites were the mediating functions of this shift. A picture of the dynamic processes taking place in peripheral layers during grain development was obtained in this study. It should further help in the construction of proteome reference maps for the developing peripheral layers.