普通小麦是由二倍体节节麦（DD genome）和栽培四倍体小麦 (AABB genome)经杂交和染色体加倍形成的异源六倍体。在小麦形成前，其二倍体和四倍体祖先已独立进化数十万年，选择压力的巨大差异可能已经将二者雕琢成完全不同的生理系统。异源六倍化后两个完全不同的生理系统融合，生理代谢特点将如何变化？进化过程中又将如何演化？对这些问题的解析无疑对理解小麦进化具有重要意义。本项目拟用小麦的二倍体和四倍体祖先人工合成六倍体小麦来模拟普通小麦的瞬时形成过程；通过比较合成小麦与自然六倍体小麦的差别来分析长期进化的影响，也使用抽提四倍体小麦（将六倍体的DD染色体抽离）与其六倍体供体、自然四倍体相比，来探讨长期进化过程中AB亚基因组发生哪些变化。我们前期工作已经证明，六倍化后小麦根生物量和氮利用效率都明显增加。本项目拟利用上述材料，研究小麦六倍化过程中，这两个关键表型变异的生理生化机制，二者是否关联。

Common wheat is a young allohexaploid species that arisen through hybridization and chromosome doubling of cultivated tetraploid wheat (Triticum turgidum, 4n=28, AABB genome) with the wild grass Aegilops tauschii Coss. (2n=14, DD genome). Physiological systems of cultivated tetraploid wheat and wild Ae. tauschii independently evolve, undergoing distinct selective pressures for several hundred thousand years. Differentiated physiological metabolism traits have probably been sculpted. It is interesting that, after merging AABB and DD genomes, how physiological metabolism traits respond and behave and how the altered traits will evolve during its subsequent evolution process. It is important for understanding of wheat evolution. Some synthetic allohexaploid wheats produced by crossing cultivated tetraploid wheat with wild diploid grass ( Ae. tauschii, genome DD), natural hexaploid bread wheats, and a ploidy-reversed wheat (extracted tetraploid wheat) were used in main experiments of the present work. We compared the metabolism traits of synthetic allohexaploid wheats with their parental genotypes to understand the instantaneous effects of allohexaploidization. Also, we compared the synthetic allohexaploid wheats with natural hexaploid wheats to get insights into the evolution and domestication. To construct extracted tetraploid wheat, the AABB component from a common wheat line were extracted by hybridization to a tetraploid wheat, followed by repeated backcrossing to this common wheat as the recurrent parent. In theory, “extracted” tetraploid wheat with a genomic composition of AABB that is virtually identical to the BBAA subgenomes of its common wheat donor. It is ideal mode for investigating how AABB component of common wheat behaves during its long term evolution process comparing “extracted” tetraploid wheat with its common wheat donor and natural tetraploids. In this work, we plan to focus on two key phenotypes, root biomass and nitrogen use efficiency, because we observed that both root biomass and nitrogen use efficiency were enhanced after allohexaploidization in our previous research. We will investigate the physiological mechanisms of enhancements of root biomass and nitrogen use efficiency during wheat allohexaploidization, and also will consider whether the change of nitrogen use efficiency is related to root trait evolution.