玉米籽粒特异线粒体蛋白Dek-kmp调控粒重的分子机制研究

Maize (Zea mays) is an important food and economic crop. Yield improvement is the main purpose of the researches on maize. Kernel weight is one of the most important traits for yield improvement. Maize defective kernel (dek) mutants seriously disturb the development of kernel and are important material for understanding the kernel weight regulation mechanism. Numbers of dek mutants were cloned and characterized, and most of the corresponding mutant genes are mitochondrial function related housekeeping genes, indicating that mitochondrial function is critical for kernel development and kernel weight regulation. In our study, a newly identified maize dek mutant, dek-kmp (kernel-specific mitochondrial protein), was cloned by Mutator tag isolation and sequencing, as well as allelic test. The kernel weight of dek-kmp mutant was dramatically down-regulated. The mutant gene encodes a kernel-specific mitochondrial protein. Based on these data, in this study, we will conduct in-depth researches on dek-kmp mutant by in-depth phenotypic analysis, gene feature characterization and gene biological function analysis, in order to reveal the molecular mechanisms for the phenotypic appearance of dek-kmp mutant and the potential usage of Dek-kmp gene for breeding. This study will finally provide important new clue for understanding the kernel development and kernel weight regulation mechanism.

玉米是重要的粮食和经济作物，增加产量是现阶段玉米研究的主要目标。粒重是影响玉米产量的重要因素。籽粒发育缺陷（dek）突变体是研究粒重调控的重要材料，而现已克隆并鉴定的dek突变体表明线粒体功能对籽粒发育和粒重调控至关重要。本研究前期自主创制并鉴定了一个全新Mutator转座子插入突变体材料dek-kmp（kernel-specific mitochondrial protein），该突变体粒重显著降低。Dek-kmp蛋白为籽粒特异表达的功能未知线粒体蛋白，因此其应有别于以往鉴定的持家基因而对粒重调控发挥特异关键作用。本研究将在克隆了Dek-kmp基因的基础上，完成突变表型分析、基因特性分析、基因功能分析，来解析突变体调控线粒体功能并影响粒重的分子机制，及其在产量改良方面的应用潜力。该研究将为解析影响玉米籽粒发育和粒重调控的核心生物学机制提供新的线索。

玉米籽粒发育是影响玉米产量的重要因素，而线粒体是细胞氧化呼吸的重要场所。该项目新鉴定的玉米dek44突变体具有胚致死的小籽粒表型。通过Mutator标签分离法克隆了Dek44基因，其编码一个50S核糖体蛋白。通过亚细胞组份分离和线粒体核糖体分离实验确认DEK44为线粒体核糖体蛋白MRPL9。该蛋白仅在籽粒中积累。DEK44功能缺失影响线粒体编码和核编码呼吸链基因的表达。突变体中线粒体呼吸链组装显著减少，线粒体形态发生受到严重影响。突变体还影响细胞周期蛋白的表达，进而影响细胞增殖和籽粒发育。该工作首次研究了籽粒特异表达蛋白突变造成籽粒发育缺陷的机制，也是首次在禾本科作物中研究线粒体核糖体蛋白突变所造成的生物学效应。