水稻四倍体背景下非整倍体在不同非生物胁迫条件下的适应潜力及其遗传基础和生物学意义

Polyploidization is known to have ubiquitously occurred in the evolutionary histories of higher plants, and is thought to be a pervasive driving force in evolution. Likewise, aneuploidization as a large-effect mutation profoundly affects gene expression and is documented as an important driving force for rapid adaptive evolution in microbes under selective conditions. Recent studies have shown that aneuploidy generally associates with nascent polyploidization. Nonetheless, the biological significance of these aneuploidies, such as their potential roles in the adaptation of newly formed polyploids and longer-term genomic evolution of established polyploid species, remains unknown. In this proposed study, the synthetic tetraploid rice populations that have been generated and propagated will be subjected to abiotic stress experiments. The rice tetraploids were previously generated by crossing two standard laboratory cultivars, Nipponbare and 93-11, that represent the two subspecies, japonica and indica, respectively, of Asian cultivated rice (Oryza sativa L.). By using comparative oligo-FISH analysis, whole genome re-sequencing and transcriptome sequencing, we aim to investigate (1) adaptive differences of the tetraploid rice population relative to its diploid parental lines under several abiotic stress conditions; (2) adaptive potential of aneuploidy in tetraploid rice background under different stress conditions and the genetic basis of stress-tolerance; and (3) probability to impart the stress-tolerance from the aneuploidies to their euploid tetraploid progenies, and the feasibility to transfer the stress-tolerance to diploid rice by recurrent backcrossing.

多倍化是植物进化的重要机制和动力。研究表明，非整倍体在新形成多倍体中普遍发生。非整倍体是微生物在选择压力下快速适应性进化的途径之一。然而，非整倍体在植物多倍体形成早期适应和基因组进化中是否具有生物学意义一直缺乏研究。本项目拟利用前期通过典型籼、粳二倍体水稻杂交和加倍创制的四倍体后代群体及其二倍体双亲群体为实验材料，在正常以及盐和冷两种胁迫条件下，利用双色Oligo-FISH技术、基因组重测序和转录组测序，深入分析胁迫条件下不同倍性水稻群体的适应性差异、四倍体群体核型组成变化、四倍体非整倍体抗性机制；探讨抗性是否可遗传给整倍体后代和转移给二倍体水稻，具体包括：1）水稻四倍体自交后代与二倍体亲本在群体水平上适应性差异；2）水稻四倍体非整倍体在胁迫条件下表现出更强适应性的遗传基础和可能机制；3）抗性四倍体非整倍体将抗性遗传给整倍体后代的可能性，以及通过回交将四倍体抗性转移给二倍体水稻的可行性。

多倍化在自然界中广泛发生，贯穿几乎所有开花植物的进化历程，也被普遍认为是物种进化的重要机制和动力。在多倍体植物中，由于减数分裂过程的存在，染色体数量及结构变异十分普遍。染色体数量变异通常会导致非整倍体的产生，非整倍体已被证实是微生物在选择压力下快速适应性进化的途径之一。近期多项研究表明，新形成的植物多倍体群体中常伴随大量的非整倍体出现，然而，非整倍体在植物多倍体形成早期适应和基因组进化中是否具有生物学意义一直缺乏研究。.本论文使用一套人工合成水稻籼粳亚种间四倍体的自交早代（S5）群体作为实验体系，利用盐、冷两种可致死的非生物胁迫来评估四倍体自交早代群体与其二倍体双亲群体间的抗逆性差异，并结合水稻双色寡核苷酸荧光原位杂交（Oligo-FISH）和重测序技术评估了四倍体自交早代群体中对照群体和盐、冷抗性群体的核型组成分布，以评估在水稻籼粳亚种间四倍体背景下，非整倍体是否在非生物胁迫环境中具有更强的适应潜力。实验结果表明，S5代四倍体盐抗性群体中非整倍体比例与对照群体相比虽然显著降低，而S5代四倍体冷抗性群体的非整倍体比例与对照群体和冷敏感群体相比无显著性差异。但非整倍体盐抗性个体的大概率是染色缺失体的非整倍体，而非整倍体冷抗性个体更多的是染色体增加的非整倍体。其中，9号和7号染色体的缺失对盐抗性的产生有密切关联，而11号染色体的增加对冷抗性的产生有着重要贡献。.综上所述，虽然高盐和冷胁迫条件下，四倍体存活群体中非整倍体比例并没有显著升高，但其中的非整倍体抗性单株却表现出了个别染色体的富集现象，这也暗示着非整倍体作为新形成多倍体繁殖过程中无法避免的中间产物，对抗逆性表型的产生有着非常重要的作用，而且非整倍体可以将在当代产生的影响传递给其整倍体后代，对群体的多样性、对新环境的适应性都有促进作用。