生长素在拟南芥种子发育过程中的分布模式及功能的研究

Auxin is an important plant hormone, which plays key roles in plant development. The distribution patterns of auxin in root, embryo, male and female gametophytes have been characterized and the mechanism of its establishment and function has been revealed. However, the distribution pattern of auxin during seed development and the underlying mechanism have not been uncovered. Seed consists of three genetically distinct constituents: seed coat, endosperm and embryo. For proper seed development, these three structures have to develop in a highly controlled and co-ordinated manner. We hypothesize that auxin is a key regulator in synchronizing these three organs’ development. Using the auxin responsive reporter DR5:GFP, we found that auxin response increased as seed develops, then the signal became weaker when seeds started to desiccate. Furthermore, auxin distribution is asymmetric during seed development. At the early seed developmental stages the auxin maximum localized to the funiculus and the chalazal seed coat (placentochalaza), while at the later stages the auxin maximum was restricted to the chalazal seed coat. We will use fluorescent protein fusions of auxin biosynthesis and polar transport pathway to determine how this auxin asymmetric distribution is established, whether it is correlated with location-specific auxin biosynthesis, or it is the results of auxin polar transportation. Furthermore, we will use auxin biosynthesis mutants and auxin polar transport pathway mutants to analysis whether this auxin gradient is affected in these mutants and whether their seed coat, embryo and endosperm development are defective. We will also use seed tissue specific promoters, such as seed outer integument cell layer specific promoter, micropylar end seed coat specific promoter to manipulate the auxin distribution, and analysis whether and how the seed coat, embryo and endosperm development are affected. This work will provide insights into the role of auxin in coordinating seed coat, embryo and endosperm development.

生长素是重要的植物激素，调控植物生长发育的各个方面。根、胚、和雌雄配子体发育过程中生长素的分布模式已有详细研究，并基本阐明了其建立机制及功能。但是，种子发育过程中生长素的动态分布、建立机制及功能还不清楚。种子由种被、胚和胚乳组成，种子的发育需要受精的诱导，而且种被、胚和胚乳的发育必须协调一致，才能保证植物顺利繁殖。已知受精作用诱发了种子中生长素响应的增强，我们推测生长素在调控三者的协调发育中起着重要的作用。我们利用响应生长素的分子标记DR5:GFP研究发现，随着种子的发育生长素含量逐渐升高，种子成熟开始脱水时又逐渐降低，而且，其在种子中的分布是不对称的，发育早期其最大分布位于种子柄和合点端种被，而后期则位于合点端种被。将利用生长素合成和运输途径的分子标记分析种子中生长素极性分布是由本地合成还是极性运输建立起来的，并利用相应的突变体，以及种子组织特异表达的启动子研究这种极性分布的生物学功能。

生长素在植物各个组织不是均匀分布的，而是存在着浓度梯度。而且，生长素的这种极性分布对其调控植物组织、器官的发育至关重要。拟南芥根、侧芽、胚、和雌雄配子体发育过程中生长素的分布模式已有详细研究，并基本阐明了其建立机制及生物学功能。但是，种子发育过程中生长素的动态分布、建立机制及功能还不清楚。种子是粮食作物收获的重要器官，研究其发育过程中生长素的分布模式和作用机理具有重要的理论和应用意义。本项目首先利用响应生长素的分子标记DR5:GFP和DR5:GUS，研究了种子发育过程中生长素的分布模式。结果发现：随着种子的发育，生长素含量逐渐升高，种子成熟开始脱水时又逐渐降低；而且，生长素在种子中的分布是不对称的，发育早期其高点位于种子柄和合点端种被，而后期则位于合点端种被。本项目随后研究了生长素合成相关基因包括ASA1、ASB1、TAA1和YUC基因在种子发育过程中的表达情况。同时还分析了生长素外输载体PIN蛋白和内输载体AUX1蛋白在种子发育过程中的表达和定位情况。结果表明：种子发育过程中生长素的极性分布是由生长素本地合成和极性运输共同作用建立起来的。并利用生长素合成和运输途径基因的突变体对上述结果进行了验证。在相应的生长素合成和极性运输突变体种子中，DR5:GFP和DR5:GUS在合点端种被的表达水平明显降低。我们进一步利用组织特异性启动子，驱动YUC基因和PIN基因在种子的不同组织表达，干扰种子发育过程中生长素的极性分布，从而研究种子中生长素极性分布的生物学功能。本项目的研究结果将为通过调控种子发育过程中生长素的合成和运输，提高农作物的产量提供重要的理论依据。