甜菜碱促进转基因番茄果实增大机理研究

Tomato (Solanum lycopersicum Mill.) represents a model species for all fleshy fruits, and is also an important vegetable crop. Modification of the growth and development of fruit has crucial role on increasing yield of tomato plants. Glycinebetaine (GB) is known as compatible solute, a particularly effective protectant against abiotic stress. GB is synthesized from choline, and betaine aldehyde dehydrogenase (BADH) and choline oxidase (COD) are key enzymes in the synthesis of GB. Our previous study found that the presence of the codA transgene and BADH transgene clearly resulted in increased sizes of flower buds and flowers under normal conditions, The ripe fruits of transgenic tomato plants were also considerably larger and heavier than those of wild-type plants, indicating that glycinebetaine may has a new function on fruits development and size. In this research, we will use two kinds of transgenic plant, which can accumulate glycinebetaine in vivo, the BADH transgenic tomato and codA transgenic tomato plants as test materials to study the mechanism of glycinebetaine in increasing the fruit size of tomato. The photosynthetic characteristic of transgenic plants and wild type plants will be analyzed, theses including photosynthetic rate, the activities of key enzymes of carbon reaction, and the accumulation of photo-assimilates. Meanwhile we will test the photo-assimilates export and allocation to tomato fruits and the partition of sugar to fruits between the transgenic and wild type tomato plants. In order to explore the molecular mechanism of GB on the growth and development of tomato fruits, the expression of key fruit growth-related genes in tomato will be tested, these including genes regulating cell cycle and endocycle, genes controlling fruit size, and genes involving in the carbon reaction, sugar transport and partition will be tested in transgenic and wild type tomato plant. In brief, we will explore the mechanism of GB on fruit size in source and sink activity, the regulation of genes and phytohormone. These researches will explore the physiological and molecular mechanisms of glycinebetaine in increasing the fruit size and provide some basis of strategies to increase yield of crop by biotechnology.

番茄是重要的蔬菜作物，也是肉质果实的模式植物，研究番茄果实生长发育的调控机制对于提高番茄产量具有重要的科学意义。我们前期研究发现，甜菜碱除具有提高植物对多种逆境胁迫的抗性外，还具有促进番茄果实增大的新功能，但其作用机理尚不清楚。本研究拟在前期研究基础上，以已经获得的转甜菜碱脱氢酶（BADH）基因番茄和转胆碱氧化酶（codA）基因番茄（野生型番茄本身不能合成甜菜碱，转BADH和转codA基因番茄体内能够合成甜菜碱）为材料，利用光合测定、酶学分析、同化物代谢以及基因和蛋白表达分析等方法和技术，从番茄叶片光合作用、同化物运输及分配、果实中蔗糖的代谢等方面，从代谢源和代谢库特性及源-库调节、基因表达及激素调控等层面，系统研究甜菜碱促进转基因番茄果实增大的调控网络及生理和分子机制。研究结果将揭示甜菜碱促进番茄果实增大的作用机理，为提高作物产量的基因工程提供新的理论依据。

番茄是重要的蔬菜作物，也是肉质果实的模式植物，研究番茄果实生长发育的调控机制对于提高番茄产量具有重要意义。我们前期研究发现，甜菜碱除具有提高植物对多种逆境胁迫的抗性外，还具有促进番茄果实增大的新功能，但其作用机制尚不清楚。本研究在前期研究基础上，以转甜菜碱脱氢酶（BADH）基因番茄和转胆碱氧化酶（codA）基因番茄（野生型番茄本身不能合成甜菜碱，转BADH和转codA基因番茄体内能够合成甜菜碱）为材料，从番茄叶片光合作用、同化物运输及分配、果实中蔗糖的代谢等方面，在代谢源和代谢库特性及源-库调节、基因表达及激素调控等层面，研究了甜菜碱促进转基因番茄果实增大的生理和分子机制。研究结果表明：（1）与野生型番茄相比，转基因番茄果实明显增大，而且果实的心室、胎座、果柄细胞的体积明显增大。（2）转基因番茄植株的叶片数量和面积显著增加。转基因番茄叶片具有更高的净光合速率，白天积累更多的碳水化合物，碳水化合物的夜晚消耗量高于野生型番茄叶片，为果实的生长发育提供充足的营养物质。（3）转基因番茄果实蔗糖、果糖、葡萄糖和淀粉的含量显著提高，糖代谢关键酶活性较高，有利于果实中碳水化合物的代谢与积累。（4）与野生型番茄果实相比，转基因番茄果实中生长素、细胞分裂素、赤霉素等植物激素的含量均显著升高。（5）转录组结果表明，甜菜碱通过调控基因的表达来促进番茄果实的生长发育，尤其是诱导番茄SlCIPK7、SlSTK、SlIAN9和SlAGL11基因的表达，参与调控信号转导、转录和翻译等过程，影响蛋白质的生物合成，从而促进番茄果实的增大。（6）转基因番茄果实的半胱氨酸和甲硫氨酸代谢通路发生明显的转录与代谢变化，甲基转移酶、甲基化调控等基因存在差异性表达，表明GB在番茄体内可能作为甲基供体参与调节重要的甲基化过程，调控番茄植株中相关基因的表达，从而促进番茄花和果实的生长发育。研究结果较系统揭示了甜菜碱促进番茄果实增大的作用机制，为提高作物产量的基因工程提供新的理论基础。