耐旱蓝藻发菜WSPA蛋白对胞外多糖胶鞘结构稳定性的调控作用研究

发状念珠藻，俗称发菜，生长于我国西北荒漠地带，对干旱逆境具有极强的适应性。发菜在经受干湿交替变化时，其原植体发生剧烈的收缩和膨胀，电镜观察发现，复水时发菜胞外多糖膨胀成网格状，干燥时细胞被保护于收缩多糖的孔隙中，因此胞外多糖结构的弹性和刚性的稳定调节对发菜细胞的生长和耐旱形成了重要保护，但其调节的分子机制还不清楚。WSPA蛋白是发菜胞外多糖胶鞘中的最丰富蛋白，前期研究揭示WSPA具有β-半乳糖苷酶的水解活性、并与多糖胶鞘结构的动态调节有关。本项目拟从多个层面阐释发菜WSPA蛋白对多糖胶鞘结构稳定性的调节功能与机制，包括：WSPA的转糖苷合成活性及各种影响因素的分析；借助遗传手段等重点探究WSPA在发菜“膨胀与收缩”中对多糖胶鞘结构调节的理化特征变化；分析胶鞘中其它重要组分与WSPA的互作与协同作用。本项目研究将拓深对发菜适应环境逆境机制的认识，并将为利用发菜改良荒漠生态提供一定的理论指导。

Terrestrial cyanobacterium of Nostoc flagelliforme, commonly known as “Facai”, is distributed in arid steppes of northwest China. There its thallus undergoes periodic rewetting and desiccation cycles, and correspondingly the thallus expands and contracts acutely in diameter. Ultrastructural observation revealed that the extracellular polysaccharide (EPS) matrix expands to be grids when rehydrated, while it shrinks with cells being embedded in protective voids when desiccated. Thus the stable alteration of elasticity and rigidity of EPS matrix should play critical protection for cell growth and drought resistance. However, the molecular mechanism underlying this regulation is unclear. WSPA protein was found to be the most abundant protein in EPS matrix of N. flagelliforme; biochemical analysis revealed it has beta-galactosidase activity, and in vitro experiment found that it is correlated to the dynamic regulation of the structure of EPS matrix. Based on these backgrounds, this project intends to explore the concrete roles and mechanisms of WSPA protein in maintaining structural stability of EPS matrix from several aspects, including: To investigate potential transglycosylation activity of WSPA and the affecting factors; With the help of genetic means etc., to clarify the detailed processes and features of WSPA in shaping the structure of EPS matrix during expansion and contraction; To investigate potential synergistic functions of other important matricial components with WSPA in EPS matrix. This research will help gain more insights into drought adaptation mechanisms of N. flagelliforme in arid environments and also provide useful guidance for future application of this species in the improvement of desert ecosystem.