BTZ基因家族调控花器官发育稳态的功能进化研究

In contrast to morphological plasticity of vegetative development in plants in response to various environmental changes, the development of reproductive traits, like floral organs, often show phenotypic robustness against environmental variations. However, it still remains obscure about the molecular basis of floral developmental robustness. BTZ is one core component of the exon junction complex (EJC), and it plays significant roles in mRNA metabolism processes. In our previous studies, we found that both gene expression and protein subcellular localization of plant BTZ family were obviously altered in response to stresses, such as salinity stress. Moreover, transgenic analyses revealed that BTZ genes from Oryza sativa were involved in floral developmental robustness in certain environments, while the ortholog of rice BTZ genes from Physalis floridana exerted an essential role in pollen development, suggesting functional divergence of plant BTZ genes in floral developmental robustness which is dependent of environments, thus a likely adaptive role of this gene family in plant evolution. In this proposal, we are suggesting to focus on molecular mechanisms controlling floral developmental robustness by BTZ genes in rice via RNA-seq, RIP-seq analyses in various BTZ transgenic rice plants relative to wild-type rice. We also will elucidate the functional divergence of plant BTZ genes through comprehensive comparisons in protein–protein interaction network, gene expression patterns in floral organs, and differentiation in target genes of paralogous genes in rice and orthologous genes between rice and P. floridana. Further correlation analysis between floral organ phenotypic variation of transgenic plants and multiple environmental factors will be performed to understand the adaptive role of BTZ gene family in plants. The achievements of this study will provide new insights into understanding the molecular mechanisms underlying floral developmental robustness and its adaptive evolution.

在不同环境下植物营养生长往往呈现出很强的表型可塑性，而生殖生长，如花器官发育，则呈现出较强的稳态性。目前尚不清楚花器官发育稳态的调控机制。BTZ是外显子拼接复合体核心成员之一，它在RNA代谢中起重要作用。我们前期研究表明，BTZ基因的表达及其编码蛋白的亚细胞定位对胁迫有明显应答变化。转基因分析表明水稻BTZ基因参与依赖于环境的花器官稳态调控，而毛酸浆中该基因主要决定花粉发育。这些结果表明植物BTZ基因在花发育调控中呈明显的功能分化并具有适应性功能。所申请项目将通过RNA-、RIP-seq等分析水稻BTZ转基因植物，聚焦解析该基因参与花发育稳态的分子机制；通过蛋白互作网络、表达模式、靶基因等全方位比较分析，揭示水稻和毛酸浆中（直系和旁系）同源基因的功能分化机制，并结合花器官表型变异和环境因素相关性分析，理解BTZ基因家族的适应性进化机制。研究结果将为阐明花发育稳态及其适应性的机制提供新认识。

本项目基本按计划执行，获得了预期结果，达到原定目标。主要研究进展总结如下。在不同环境下植物营养生长往往呈现出很强的表型可塑性，而生殖生长，如花器官发育，则呈现出较强的稳态性。目前尚不清楚花器官发育稳态的调控机制。BARENTSZ（BTZ）是外显子拼接复合体（exon junction complex, EJC）核心成员之一，它在mRNA代谢中起重要作用，调控动物多种发育过程。然而，其在植物中的进化和发育作用尚不清楚。全基因组分析表明，BTZ起源于真核生物，在蓝星睡莲中有发生了基因重复，但在37.66%的物种中只存在一个拷贝。禾本科中两个BTZ序列的序列一致性（~35%）极低，表明BTZ基因家族在禾本科中存在极大的功能分化，是一种特殊的进化模式。为此，我们编辑了水稻中两个基因OsBTZ1和OsBTZ5，发现它们每个基因的突变体呈现出相似的多种花形态缺陷。而且，osbtz1/5双基因突变体呈现相同的花器官异常类型，但变异花的比例和变化程度更为明显，暗示水稻两个BTZ基因在维持花稳态发育中发挥重要作用并存在加性效应。特别地，OsBTZ在雄蕊发育中具有重要作用。特别有趣的是，osbtz突变体的花形态和功能缺陷在低温下表现得尤为明显，体现出明显的温度变化依赖性。综上所述，水稻序列高度分化的两个BTZ旁系同源基因平行参与花的发育和功能决定，维持花的稳态发育，并在调控应对温度变化诱导的花发育可塑性中发挥关键作用。以上研究结果为研究重复的EJC基因在植物发育和适应进化中的功能分化提供了新的思路，为理解BTZ基因家族的适应性进化机制。