玉米心皮融合不完全子房对激素调控的响应机制

Kernel is an important economic organ for maize. When the pericarp of kernel is incomplete, the embryo and endosperm are susceptible to infection of pathogenic bacteria, affecting the activity and economic value of the seed. The pericarp of the kernel is derived from fusion of three carpels, which form the pistil, and the complete carpel fusion is of great importance to pistil formation and kernel development in maize. It has been proved that the incomplete carpel fusion results in gaps on the ovary and kernel; reduction in kilo-grain weight and contents of cytokinins, gibberellins, and brassinosteroids; but increase in auxin content, and significant difference in genes related to hormone metabolism. In this project, the research will use the same inbred lines to study the dynamic changes in structure, number, shape and size of the carpel marginal cells during carpel fusion, and in contents of plant hormones to understand the process of pistil formation. This research intends to explore the effects of exogenous auxin or auxin inhibitors treatments on carpel fusion and expression of genes related to hormone metabolism, to analyze the effects of synthesis, transportation and distribution of auxin on carpel fusion, and then to explain the molecular mechanism how the pistil is formed through carpel fusion and how carpel fusion responses to hormone regulation. These results will help to clarify the morphological, physiological and molecular mechanisms of carpel fusion during ovary formation, and provide a theoretical basis for kernel development and yield-increasing of maize.

籽粒是玉米重要的经济器官。籽粒果皮不完整时胚和胚乳易受病原菌侵染，影响种子活性及经济价值。玉米果皮来源于形成雌蕊的三片心皮，心皮融合完全对玉米雌蕊形成及籽粒发育具有重要意义。项目申请人前期研究证明：玉米心皮融合不完全时，雌蕊子房和籽粒果皮有缺口；千粒重降低；生长素含量显著升高，细胞分裂素、赤霉素、油菜素内酯等含量显著降低，生长素等激素代谢相关基因表达差异显著。本项目拟在上述研究基础上，以籽粒果皮有缺口自交系为材料，研究玉米心皮融合发育过程中，心皮边缘细胞的结构、数目、形态、大小等变化，以及六大类植物激素的动态变化；同时探究外源喷施生长素、生长素抑制剂，对心皮融合不完全的缓解作用及对激素代谢相关基因表达的影响；进一步研究生长素在雌蕊中的合成、运输和分布及其与心皮融合的关系。从而阐明玉米子房形成时心皮融合发育的形态、生理和分子机制，为玉米籽粒发育和高产提供理论基础。

玉米籽粒产量的形成和提高依赖于雌穗上雌蕊子房的正常形成、受精和发育。玉米雌蕊子房由三片心皮融合发育而来，心皮壁发育为籽粒的果皮。但当心皮融合不完全时，玉米籽粒表现为果皮缺陷即果皮有缺口，这种籽粒易受病原菌侵染而发霉，严重影响玉米籽粒的品质。本项目通过对玉米雌穗小花的雌蕊形成时心皮融合发育的动态结构观察发现，心皮融合缺陷雌蕊的第三片心皮顶端细胞短小，第三片心皮纵向伸展受阻，发育缓慢，最终第三片心皮与另两片融合形成雌蕊花柱的心皮之间发育不一致，致使第三片心皮不能同步与另外两片心皮进行融合，三片心皮间的融合发育出现缺口。通过对心皮融合过程中不同时间点的子房取样测序分析发现，富集到花发育、性器官建成、激素代谢、转录调控等功能上的差异基因是调控雌蕊子房形成时心皮融合的核心基因，通过将这些基因与控制拟南芥中心皮融合调控基因的氨基酸序列比对发现7个基因氨基酸序列相似度达75%以上，说明这些基因在玉米雌蕊心皮融合发育过程中起到至关作用。此外，通过外源喷施生长素显著缩短了植株的营养生长期，使生殖生长提前，缓解雌穗上子房形成时心皮融合缺陷性状有一定的作用，但并不能彻底解决心皮融合缺陷症状。这表明生长素确实在玉米雌穗雌蕊心皮融合形成发育过程中发挥积极的作用，生长素代谢路径中相关的差异表达基因及调控基因功能的深度挖掘将为揭示玉米雌蕊形成发育发挥重要作用。