玉米BSD2基因调控维管束鞘细胞和叶肉细胞叶绿体发育机理的研究

In recent years, the International Rice Research Institute (IRRI) proposed the C4 rice project, which will engineer the C4 photosynthetic machinery into rice to improve the yields of rice and ensure future global food security.Maize is a typical C4 plant, to study its special C4 photosynthesis mechanism is of great theoretical and practical value to improve the photosynthetic efficiency of crop and the world food yield. So studying C4 photosynthesis mechanism of maize is particularly urgent.BSD2 is a chloroplast chaperone protein and has high homology in C3 rice and C4 maize. It plays important roles in chloroplast morphogenesis and photosynthetic regulation.This program will approach four major contents by comparing wild type and bsd2 mutant maize: 1) to explore the function of BSD2 gene in Rubisco biosynthesis and holoenzyme assembly in C4 photosynthetic system, 2) to study the regulation of BSD2 gene on plastid division in C4 chloroplasts development, 3) to study the regulation of BSD2 gene on grana biosynthesis of C4 chloroplasts, 4) to explore the different mechanism of BSD2 gene on regulation of chloroplast development in maize bundle sheath and mesophyll cells. By researching BSD2 gene, this program will reveal the mechanism of C4 chloroplasts development at cytological and molecular level, and will provide a significant theoretical guidance for helping rational design of C4 rice in future studies.

近年来国际水稻研究所提出了C4水稻工程，拟通过引入C4光合机制改进水稻内部光合过程，以达到水稻高产和确保未来粮食安全的目的。玉米是典型C4植物，研究其特殊C4光合作用机制对提高作物光合效率和世界粮食产量具有重大价值。BSD2是叶绿体分子伴侣蛋白，在C3水稻和C4玉米中具有高度同源性，对叶绿体形态建成及光合机制调控影响重大。本项目以野生型和bsd2突变型玉米为研究材料，重点开展以下工作：1)探讨BSD2基因在玉米C4光合机制Rubisco合成/组装中的功能；2)玉米C4叶绿体发育过程中BSD2基因对质体分裂的调控作用；3)玉米C4叶绿体发育过程中BSD2基因对基粒合成的调控作用；4)探讨在玉米鞘细胞和叶肉细胞中BSD2基因影响叶绿体形态发育的不同调控机制。本研究能更好地了解BSD2基因影响玉米C4叶绿体生物合成的细胞学和分子生物学调控机制，同时可为探讨C4水稻的未来研究提供更充分的基础资料。

玉米bsd2为典型的碳四突变体，光合作用缺失，同时伴随着Rubisco积累的减少和维管束鞘中成熟叶绿体形态的破毁。然而，虽然推测BSD2是叶绿体分子伴侣蛋白，但是其对碳四植物叶绿体发育的影响并无系统报道，严重妨碍了人们对其在碳四光合作用中的功能的全面评估。本研究的目的就是揭示BSD2在玉米叶中调控叶绿体发育的作用机制，为深入了解碳四植物生物学提供了新的资料。.我们的研究发现，在叶绿体成熟阶段，与野生型相比，bsd2突变体中维管束鞘和叶肉叶绿体的内囊体膜变得非常疏松，基粒宽而薄。而且，在叶绿体发育的早期阶段，进行分裂的叶绿体数目和分裂速率在突变体中明显低于野生型的情况。定量PCR分析揭示出内囊体形成相关基因和叶绿体分裂相关基因的表达量在突变体中显著降低。进一步地我们利用酵母双杂交和免疫荧光共沉淀技术证明了BSD2与Rubisco大亚基互作。我们的结果指出BSD2在调控维管束鞘和叶肉细胞中二型叶绿体的分裂和分化 中发挥了重要作用，可能在过转录水平调控着Rubisco大亚基的稳定或者组装。