太行花雄全同株性系统的维持机制及其适应意义

Plant diverse sexual systems have been employed as a model to study the evolution and adaptation of plant reproduction. It has been suggested that andromonoecy is an intermediate type in the evolution of a plant sexual system from hermaphroditism towards monoecy and dioecy. However, the maintenance and adaptation of this sexual system have not been fully understood. In order to improve understanding of this plant sexual system, this project focus on effects of genetic and environmental factors on sex expression and allocation among male and hermaphroditic flowers in an andromonoecious plant species Taihangia rupestris (Rosaceae). The main contents of the proposed study are as follows: Investigating spatial-temporal variations of sex expression, and revealing the patterns of resource allocation among male and hermaphroditic flowers; Examining floral syndrome and pollen dispersal processes in male and hermaphroditic flowers, detecting variations of mating strategy among natural populations, and further determining whether male and hermaphroditic flowers contribute equally to successful reproduction; Effects of genetic and environmental factors on frequency of male and perfect flower will be analyzed in transplanted population under controlled condition to clarify the dominant factors that play key role in controlling patterns of sex expression and allocation; Using hand pollination, androgamete selection of perfect flower will be tested by paternity analysis, and further will examine whether there are different fitness among selfing and outcrosing progenies. The proposed study will clarify the function of male and hermaphroditic flowers and interaction between genetic and environment factors and sex expression. The project will be helpful not only to elucidate the maintenance mechanism and reproduction adaptation in andromonoecious sexual system, but also to improve our understanding of evolution and adaptation of diverse plant sexual systems in nature.

植物多样化性系统已成为研究植物进化与适应的模式系统。雄全同株被认为是由雌雄同花向雌雄同株或异株等性系统演化过程中的中间类型，但对其维持及适应还缺乏统一认识。为此，本研究拟对雄全同株植物太行花的性表达及其影响因素进行研究，内容包括：调查太行花性表达的时空特征，揭示雄花、两性花的资源配置模式；比较分析雄花和两性花的花部综合特征、花粉散布、传粉过程以及交配策略，揭示雄花、两性花对成功繁殖的贡献；建立移栽群体，分析遗传因素和环境因子对太行花雄花两性花表达和配置的影响，明确影响太行花雄花性系统中两性花性表达的主导因素；设计人工授粉实验，检验雄花与两性花、自交与异交不同杂交组合对后代适合度的影响。本项目将阐明太行花雄全同株两性花和雄花的雄性功能，明确影响雄花和两性花配置的关键因素，进而探讨太行花雄花两性花同株性系统的维持机制及适应意义，完善对自然界多样化植物性系统的进化与适应的理解和认识。

本项目以雄全同株植物太行花为研究材料，对其雄花和两性花维持机制及适应意义进行了较深入研究。经过四年的野外调查及室内实验分析，本课题组已按照计划完成了项目任务。野外观测太行花的开花进程和传粉特征，运用杂交指数、花粉-胚珠比、人工授粉等方法分析太行花的繁育系统，初步明确太行花属于异交、自交并存的混合交配系统。通过调查太行花居群生境特征和性表达的时空特性，比较分析雄花和两性花的花部综合特征、传粉表现及资源配置模式，阐明了太行花雄全同株性系统的性别分配是资源限制的适应策略。运用SSR分子标记检测太行花居群的遗传结构与交配系统，并分析其与性表达的关系，表明太行花居群性比率不是影响其遗传结构和交配方式的主要因素。采用花粉竞争实验及SNP子代亲本鉴定，两性花对雄花与两性花雄配子的选择不存在偏好性，说明雄花并没有表现出比两性花更强的花粉输出优势。设计人工授粉实验，检验不同交配方式产生后代的适合度，发现各杂交组合子代在结籽率、籽粒大小、籽粒重、萌发率及存活率等方面没有显著差异，表明太行花没有表现出明显的自交衰退，自交仍然是其主要传粉方式的之一。此外，我们应用高通量转录组测序技术比较分析了雄花和两性花的基因表达模式，鉴定了太行花在性别分化中的差异表达基因主要涉及代谢过程、细胞周期、花器官发育、DNA甲基化等生物学过程，表明这些生物学过程参与了太行花雄花和两性花的发生发育和分化。我们还采用MSAP技术对太行花雄花和两性花的DNA甲基化进行了研究，发现两性花的DNA甲基化程度要高于雄花。通过DNA甲基化差异片段分离、克隆测序及功能鉴定，获取 DNA甲基化差异基因信息。运用实时荧光定量PCR技术检测其表达模式，结果显示基因DNA甲基化与其基因表达密切相关，表明DNA甲基化在太行花性别分化过程中起着重要作用。本项目研究结果对于理解植物雄全同株性系统的适应与进化奠定了基础，同时也对濒危植物的保育具有重要意义。