小麦在异源六倍化过程中非生物抗性变异及其生理学机制

Polyploidy (often referred to as whole genome duplication, WGD) has long been recognized as a major force in plant evolution, and it is now a major research focus in biology. To date, most studies have focused on the genetic, genomic and epigenetic aspects of polyploidy, while very little attention has been given to its physiological consequence and the physiological pathways leading to the adaptive variation of new polyploid. Thus, many physiological issues of polyploid evolution remain unexplored. For example, whether the adaptability of plants to particular environment is altered after polyploidization, and whether the metabolic pathway of new polyploid is altered by environment stress. Study of these physiological issues will be important for understanindg unique attributes associated with polyploidy. This proposal is aimed to address the physiological aspect of polyploidy in wheat, and will study how stress tolerance is altered by polyploidization. We will use resynthesized allohexaploid wheat (genome AABBDD) as the test organism. Specifically, we will compare the response and tolerance of resynthesized allohexaploid wheat, its diploid and tetraploid parents and natural common wheat (Triticum aestivum L.) to abiotic stresses. Contents to be studied include: (1) whether the response and tolerance of wheat to abiotic stresses(salt stress and drought) are altered after polyploidization; (2) the physiological mechanism leading to these changes. Results gained from this study may further our understanding of the physiological and biochemical attributes of plant allopolyploidy.

多倍化是指物种全基因组加倍（WGD）事件，一直是生物学领域的研究热点之一。然而，已有研究的视角几乎全都放在了遗传学、基因组学及表观遗传学等方面，而忽视了物种经历多倍化后自身生理特性的改变及其与适应性的关系。因此，多倍体形成过程中的许多生理学问题都知之甚少。例如，物种刚经历多倍化后对特殊环境（胁迫）的适应能力是否发生变化？在极端环境下（非生物胁迫）其生理代谢途径是否发生改变？这些问题的研究对揭示多倍体进化特点具有重要意义。本项目旨在从生理学层面探讨多倍化如何影响小麦抗逆性。本项目拟以人工合成异源六倍体小麦为材料，通过比较人工合成小麦、它的二倍体和四倍体亲本及自然形成六倍体小麦（中国春）的抗盐性和抗旱性，来探讨小麦在异源多倍化过程中非生物抗性（抗盐、抗旱）的变化以及这种变化产生的生理学机制。研究结果将有助于了解植物异源多倍化的生理生化本质,加深人们对多倍体生态适应性的理解。

现今普遍种植的小麦是由粗山羊草(Aegilops tauschii, genome DD)和栽培四倍体小麦(Triticum turgidum, genome AABB)经杂交和染色体自然加倍形成的异源六倍体小麦。六倍体小麦形成后，立即取代其四倍体祖先迅速传播到全世界。六倍体小麦产量略低于四倍体小麦，但却可取代四倍体小麦，主要是因为其具有广泛的适应性。目前，异源六倍体小麦适应性形成机制知之甚少。本项目从生理学层面探讨了，多倍化如何影响小麦抗逆性。本项目的主要科学发现是：六倍体小麦耐盐性是在六倍化后瞬时形成的，后续的进化和驯化贡献较小。新形成的六倍体小麦主要通过继承双亲的特性及产生超亲耐盐特性两种方式瞬时获得高耐盐性。刚形成的六倍体小麦遗传了其二倍体亲本的离子控制特性和四倍体亲本的萌发特定。进一步分析发现盐胁迫可提高D基因组的表现，提高TaHKT1;5D的表达，来实现耐盐性革新。TaHKT1;5D在小麦六倍化过程中表达模式发生了明显的变化，由原来的组成型表达变成了诱导性表达，这可能是六倍体小麦耐盐性进化的关键所在。项目研究阐述了小麦耐盐性进化的基本轮廓，发现六倍体小麦耐盐性提高的主要生理学机制。该项研究成果以第一作者发表在国际顶尖杂志PNAS(IF=9.6）上，发表后被国际生物学评论杂志Nature Reviews Genetics（IF=36.9)原图引用并评论。