叶绿体定位的假定I型DNA拓扑异构酶控制水稻强光周期敏感性的分子机理

Heading-date of rice is an important trait for the yeild and adaptation to different cultivation areas and planting seasons. Rice is a short-day plant; wild rice and many native indica rice cultivars have a nature of strong sensitivity to photoperiod on heading-date, but most japonica cultivars and modern improved indica varieties have retained only weaker photoperiod sensitivity. However, the known heading-date genes cannot explain the strong photoperiod sensitivity in rice. In previous works we have fine-mapped and cloned a gene that suppresses completely rice floral-transition under long-day conditions. This gene, NHLD (no heading under long day) encode a putative DNA topoisomerase I that targets to chrolaplasts, thus is a new type of heading-date gene. In this study we will carry out functional and mechnistic analyses on this gene: (1) Further confirmation of the function of NHLD by genetic transformations with various expression constructs；(2) Expression analysis of chrolaplast genes and other known heading-date genes affected by NHLD; (3) Screening for target genes and interactors of NHLD by gene-expression microarray and yeast two-hybridization; (4) Assay of the DNA topoisomerase I activity of NHLD; (5) Analysis of geographical distribution of naturally occurred varient alleles of NHLD in rice cultivars and wild rice speciese. The findings in this study will be significant for elucidation of the molecular mechanism on evolution of the photoperiod sensitivity during rice domestication and modern breeding, and has important implication on heading-date control and yeild improvement.

水稻是短日植物，野生稻和原始型晚籼稻品种的抽穗期具有很强的感光性，大部分现代品种只有弱感光性。而已知的水稻抽穗基因不能解释强感光性。我们在前期工作中定位克隆了一个长日下完全抑制水稻抽穗的强感光性基因NHLD (no heading under long day)，编码一个叶绿体定位的假定I型DNA拓扑异构酶，是新型的植物生殖发育基因。本研究将开展NHLD的功能和分子机理研究：（1）对NHLD进行多种表达载体遗传转化和功能分析；（2）分析NHLD与叶绿体基因和已知抽穗基因的表达调控关系；（3）研究NHLD与其它已知和未知抽穗基因的互作关系；（4）检测该DNA拓扑异构酶I的生化活性；（5）检测NHLD等位基因在野生稻和栽培稻的变异。本研究将阐明水稻驯化和现代育种过程中从强感光性向弱感光性演变和叶绿体介导的光周期逆向调控抽穗的分子机理，对控制生育期和提高产量有重要的理论意义和应用价值。

水稻是短日植物，抽穗期对光周期敏感，是非常重要的农艺性状。野生稻和原始型晚籼稻品种的抽穗期具有很强的感光性，大部分现代品种只有弱感光性。控制水稻抽穗强感光性的基因有哪些？粳稻驯化北迁和现代水稻育种削弱了原来野生稻和原始型栽培稻的强感光性的主要靶基因是什么？相关基因的作用机理是怎样的？针对这些问题，本研究对一个控制水稻强感光性基因进行了功能研究：（1）遗传转化证明了Hd1为水稻强光敏抽穗基因；（2）证明参与Hd1调控途径的基因包括Ghd7、DTH8、Ehd1和开花素基因Hd3a、RFT1；（3）发现强感光性水稻材料多携带功能型的Hd1、Ghd7、DTH8；（4）证明Hd1、Ghd7、DTH8三个蛋白之间存在两两互作；（5）利用NIL-NHLD中分别敲除Hd1、Ghd7、DTH8 转基因材料以及NIL-NHLD，开展了不同日长条件和不同时间点的转录组学研究；（6）原核表达Hd1、Ghd7、DTH8，体外筛选互作的DNA元件。本研究证明了水稻强光敏性的遗传基础需要功能型的Hd1、Ghd7、DTH8，这三个基因间存在表达调控以及蛋白水平的互作，可能通过构成复杂动态的蛋白复合体，直接结合特定的DNA元件，抑制Ehd1和开花素基因Hd3a、RFT1的表达，导致水稻产生强光敏性，长日下完全不能抽穗。本研究对控制生育期和提高产量有重要的理论意义和应用价值。