一个特殊新疆鹰嘴豆根瘤菌种群自然进化规律及其进化机制的研究

Our previous work suggested that chickpea rhizobia from Xinjiang was a distinct species, Mesorhizobium muleiense which is different from the known reported chickpea rhizobia. Furthermore after four years of natural evolution, it was still the only species M. muleiense, however not only did the increase of genotypic diversity and the dominant genotype both change a lot, but also some of the soil physicochemical characteristics also changed significantly. If it goes through much longer natural evolution, what will the species of chickpea rhizobia from Xinjiang change? What is the molecular mechanism and its driving force of the natural evolution? Technologies such as genotyping and molecular evolution analysis will be used to test the following situations in the coming three years. The dynamic changes of genotypic diversity of chickpea rhizobia and the role of gene recombination or mutation in the procedure of molecular evolution will be checked. Also the dynamic changes of the soil physicochemical characteristics will be carried out to analyze its relatedness with the dynamic changes of the species and find out the key physicochemical characteristics that affect the changes of the species. Based upon the results above, the natural evolution laws and molecular mechanism underlying the evolution of the chickpea rhizobia from Xinjiang during eight years might be revealed. In addition, the evolution driving force from outside might be illuminated.

前期研究工作表明，新疆鹰嘴豆根瘤菌是一个特殊种群：木垒中慢生根瘤菌（Mesorhizobium muleiense），与国外报道的已知鹰嘴豆根瘤菌种群不同；且经过四年自然进化，仍是唯一的种群M. muleiense，但是该种群的基因型多样性增加，优势基因型数量及土壤理化性质也发生了显著的变化。那么，如果经历更长时间的自然进化，该种群又会发生怎样的变化？其自然进化的分子机制及外界驱动力又是什么？本项目拟采用遗传分型和分子进化分析等技术手段，未来三年进一步研究新疆鹰嘴豆根瘤菌种群基因型多样性的动态变化情况，分析基因的重组及突变等在种群分子进化中的作用。然后结合土壤理化性质的动态变化情况，分析其与种群动态变化的相关性，找到影响种群进化的关键理化因子。综合上述研究结果，最终揭示在八年时间内该种群的自然进化规律及其分子机制，并阐明其进化的外界驱动因素。

本项目首次对新疆鹰嘴豆根瘤菌特殊种群——木垒中慢生根瘤菌随年份和不同采样点的自然演替进行了深入且系统地研究，结果发现：过去8年间该种群保持相对稳定，仍是唯一种群，但其recA基因型的数量增加至28个，其中优势基因型有4个，多数稀有基因型具有采样年份特异性，而且不同采样点不同采样年份基因型组成存在较大差异，其中木垒较之奇台地区的基因型更加丰富。土壤理化性质和土壤内的生物因素可能都是木垒中慢生根瘤菌种群内不同基因型自然演替和区域分布的主要影响因子。不同鹰嘴豆根瘤菌种群间的生态适应性和结瘤试验结果证明，不同的种群其生态适应性不同；木垒中慢生根瘤菌除在新疆发现之外，还发现其是甘肃省的主要鹰嘴豆根瘤菌种群；而新发现的文新中慢生根瘤菌种群目前仅在甘肃省有发现。交叉结瘤试验表明，快生型的三叶草根瘤菌不能与鹰嘴豆栽培品种卡布里结瘤。本项研究明确了中国鹰嘴豆根瘤菌种群的分布和区域自然演替规律及其机制，丰富了国际上对鹰嘴豆根瘤菌种群多样性和分布的认识，为后期深入解析鹰嘴豆根瘤菌的种间、种内竞争和生态适应性机制奠定了基础。研究工作已经在Plant and Soil杂志上发表SCI收录论文3篇，还包括奖励、著作、专利和其他论文等。