鼠李半乳糖醛酸聚糖I在番茄果实软化中的作用机制

Fruit softening regulation has been the critical topic in the reseach area of fruit and vegetable storage and preservation. Enzyme-stimulated degradation of pectin is the primary reason for fruit softening. In previous studies, we found that RG-Lyase made changes on RG-I of cell walls that led to cell separation and tissue breakdown. However, the patterns and mechanisms of RG-Lyase in regulating RG-I degradation in cell walls, as well as the close relationship with fruit texture are not clear. In this project, we will choose tomato as the model plant and generate transgenic tomato plants in which endogenous RG-Lyase is over or silence expressed to alter the structure of RG-I in tomato fruit. The relationship between RG-I and fruit softening is established by comparing the physiological changes such as firmness and texture of transgenic tomato. On this basis, on one hand we explore the molecular structural changes of plant cell wall polysaccharides of transgenic tomato fruits through GC-MS analysis. On the other hand, the cell wall polysaccharides are accurately localized by specific antibodies, combined with chemical and enzymatic digestion which selectively digest cell walls, to understand the pattern of cell wall polysaccharide cross-linking and degradation. Besides, the ultrastructure of cell walls is investigated through microscope and spectroscopy. Thus the close relationship between RG-I and texture in tomato fruit is illustrated with respect to the molecular structure and microstructure of cell walls. These results contribute to a deep understanding of pectin and are expected to provide a new way for the regulation of fruit quality.

控制果实软化一直是果蔬贮藏保鲜研究的重点，果胶酶促降解是果实软化最重要的原因。前期研究发现果胶主要成分RG-I经主链裂解酶催化降解可以增加细胞分离引起组织松散。然而RG-I降解规律以及RG-I在果实软化中的作用机制仍不清楚。本研究以模式植物番茄为研究对象，通过过表达和沉默表达果实内源RG-I裂解酶编码基因，改变果实内RG-I的存在形式，对比转基因果实硬度、质地等生理变化，建立RG-I与果实软化的关系。在此基础上，利用气相色谱-质谱分析转基因果实中果胶等多糖分子结构变化；利用多糖结合抗体结合化学和酶法定位多糖的动态分布并根据选择性降解结构推断细胞壁多糖分子交联变化模式，利用显微镜和光谱技术表征细胞壁微结构变化，综合分析RG-I在果实软化中的作用机制。研究结果可以加深对果胶的认识，有望为果实品质可控调节提供新途径。

前期研究发现果胶主要成分RG-I经主链裂解酶催化降解可以增加细胞分离引起组织松散。然而RG-I降解规律以及RG-I在果实软化中的作用机制仍不清楚。本项目重点研究RG-I型果胶在植物组织结构中的重要作用。本研究以模式植物番茄为研究对象，利用气相色谱质谱分析转基因果实中果胶等多糖分子结构变化；利用多糖结合抗体结合化学和酶法定位多糖的动态分布并根据选择性降解结构推断细胞壁多糖分子交联变化模式，利用显微镜和光谱技术表征细胞壁微结构变化，综合分析RG-I在果实软化中的作用机制。研究发现RG-I可以广泛与半纤维素、木质素交联，影响细胞间的黏连作用，从而调控组织完整性和果实硬度。并且RG-I对细胞黏连的调控广泛存在于植物体中，并根据植物细胞壁的组成结构不同而异。研究发现细胞紧密程度是决定组织完整性、果实质地的关键因素，而RG-I型果胶通过与纤维素、半纤维素交联决定细胞紧密程度。在番茄果实发育与成熟过程中，RG-I型果胶分支度越高与木葡聚糖的结合程度越广泛，细胞间紧密度越高。RG-I型果胶完整度和分支度与果实硬度呈显著正相关。RG-I型降解伴随番茄果实硬度的急速下降。RG-I型果胶在维持细胞壁完整性和致密性中也发挥重要作用，从而影响细胞壁修饰酶等小分子物质与细胞壁的接触与相互作用。为加强RG-I型果胶在植物采后生理中特别是结构质地等方面的深入认识，以木本、禾本植物杨树、红松和水稻秸秆为研究对象，重点研究在木质素-半纤维素-纤维素骨架结构下，RG-I型果胶在调节细胞黏连中的作用规律。研究发现RG-I不但在被子植物也在裸子植物细胞间黏连中的作用，说明RG-I与细胞壁其他组成多糖如半纤维素、木质素的交联作用是植物体内普遍存在的。此研究从全新的角度对RG-I型果胶进行了深入研究，为调节果实质地及高效利用纤维素基生物质提供新的思路。