Apoplastic alterations as a common mechanism to freezing avoidance and growth cessation/dormancy induction through temperature-mediated pectin gelation

植物与环境缺乏同步性是造成非生物胁迫伤害的主要原因，造成重大经济损失。植物是固定的生物，必须适应环境才能生存。在整个植物进化史上，温度一直是植物适应的关键驱动因素。然而，这些热适应的机制仍然不清楚。外胞体空间是调节冰增殖和细胞生长的关键区域。外体区是通过阿拉伯木聚糖聚合物或抗冻蛋白来避免冰直接传播到植物细胞的渗透性屏障。细胞壁部分是由凝胶状基质结合在一起的纤维素微原纤维组成的双相结构。这种凝胶状基质占细胞壁干重的三分之二（占杨树原代细胞壁的47%），由交联延伸蛋白糖蛋白和非纤维素多糖组成，包括果胶（聚半乳糖醛酸（PGAs）和鼠李糖半乳糖酸（RG） I和II）和半纤维素。果胶是决定细胞壁孔隙度的主要调控分子。胶凝、刚性和随后的外质体渗透性是由果胶基质通过果胶甲基酯酶（PME）决定的，PME去除果胶甲基，允许Ca2+结合到羧酸盐离子上，并产生钙交叉键。这种刚性和果胶形成还通过水渗透性的变化影响关键的细胞膨胀参数，如水流和膨胀压力。PME和果胶凝胶是动态的，对温度敏感，但大多数证据来自食品加工文献。值得注意的是，对植物的此类研究数量有限。该项目将通过1名博士生、1名硕士生和4名暑期本科生来解决以下首要假设：通过果胶胶凝导致的脂质改变导致：a)通过减少冰在细胞内的传播来避免冻结，b)通过减少水流来诱导温度依赖的休眠。

Lack of plant synchrony with the environment is the primary cause of abiotic stress injury resulting in significant economic loss. Plants are stationary organisms and must adapt to their environment in order to survive. Temperature has been a key driver to adaptation throughout plant evolutionary history. However, the mechanism of these thermal adaptations is still not understood. The apoplastic space represents a key region regulating both ice propagation and cell growth. Apoplastic regions are permeability barriers to avoid ice propagation directly into the plant cell through arabinoxylan polymers or Anti-Freeze Proteins. The cell wall fraction is a biphasic structure consisting of cellulose microfibrils held together by a gel-like matrix. This gel-like matrix constitutes up to two-thirds of the cell wall's dry weight (47% of primary cell walls of Populus), and is composed of cross-linking extensin glycoproteins and non-cellulosic polysaccharides including pectins (polygalacturonic acids (PGAs), and rhamnogalacturonan (RG) I and II) and hemicelluloses. Pectins are the major regulatory molecule dictating the porosity of cell walls. The gelation, rigidity and subsequent permeability of the apoplast is dictated by the pectin matrix through Pectin Methyl Esterase (PME) which removes pectin methyl groups, allowing Ca2+ binding to the carboxylate ions and creating calcium cross-linkages. This rigidity and pectic gel formation also influences key cell expansion parameters of water flow and turgor pressure through changes in water permeability. PME's and pectin gelation are dynamic and temperature-sensitive but most of the evidence comes from the food processing literature. Remarkably, there are only a limited number of such studies in plants. This project will address the following overarching hypothesis through 1 Ph.D. student, 1 M.Sc. student and 4 undergraduate summer students: Apoplastic alterations through pectin gelation result in: a) freezing avoidance by reduced ice propagation into the intracellular space, and b) temperature-dependent dormancy induction through reduction of water flow.