The Role and Regulation of Ethylene in the Cell Death Program of Maize Endosperm

在谷类种子中，淀粉质胚乳发育为储存组织，其注定在成熟前死亡，但在成熟种子中持续存在。 发育中的玉米籽粒的胚乳中的细胞死亡的进展以高度组织化的方式发生，其伴随着核酸酶活性和核DNA上的核小体间片段化的适度增加。 小麦和玉米胚乳细胞死亡程序部分受乙烯调控。 因此，分析的基因负责乙烯的生物合成和感知，以及负责DNA片段化的核酸酶将扩展我们的理解的细胞死亡程序在谷物胚乳的调节。 本项目的具体目标是：（1）研究玉米器官发育过程中乙烯生物合成和感知机制的表达，并鉴定每个基因家族的胚乳特异成员：（2）确定胚乳发育过程中细胞死亡程序启动和进行过程中乙烯生物合成和感知机制的时空调控;（3）分离ACC合酶和乙烯受体敲除突变体以遗传地表征乙烯生物合成和胚乳细胞死亡的感知的需要;和（4）表征胚乳表达的核酸酶并研究其在指导核小体间DNA片段化中的作用。 将在玉米胚乳的整个发育过程中使用RT-PCR和原位RNA定位进行表达研究。 转座子插入诱变已被用于产生影响乙烯生物合成的突变体，这些突变体将用于玉米发育过程中乙烯的表型分析。 所提出的实验将代表理解谷物籽粒发育的基本但知之甚少的方面的重大进展，这将有助于通过提供一种新的手段来提高产量，通过延长谷物种子发育期间的贮藏储备沉积的窗口来改善谷物作物。

In cereal seeds, the starchy endosperm develops as a storage tissue that is fated to die prior to maturation but persists into the mature seed. The progression of cell death in the endosperm of developing maize kernels occurs in a highly organized manner which is accompanied by a moderate increase in nuclease activity and internucleosomal fragmentation on the nuclear DNA. The endosperm cell death program of wheat and maize is regulated, in part, by ethylene. Consequently, the analysis of the genes responsible for the biosynthesis and perception of ethylene, as well as the nuclease responsible for DNA fragmentation will extend our understanding of the regulation of the cell death program in cereal endosperm. The specific aims of this project are: (1) to investigate the expression of the ethylene biosynthetic and perception machinery during maize organ development and identify the endosperm-specific members of each gene family; (2) to determine the spatial and temporal regulation of the ethylene biosynthetic and perception machinery during the initiation and progression of the cell death program during endosperm development; (3) to isolate ACC synthase and ethylene receptor knock out mutants to genetically characterize the requirement for ethylene biosynthesis and perception for endosperm cell death; and (4) to characterize an endosperm-expressed nuclease and investigate its role in directing internucleosomal DNA fragmentation. The expression studies will be carried out using RT-PCR and in situ RNA localization throughout the development of the maize endosperm. Transposon-insertion mutagenesis has been used to generate mutants affecting ethylene biosynthesis which will be used for phenotypic analysis of ethylene during maize development. The proposed experiments will represent a significant advancement in understanding a basic yet poorly understood aspect of cereal kernel development that will contribute to the improvement of cereal crops by providing a novel means to increase yield through extending the window of storage reserve deposition during cereal seed development.