Molecular mechanism of ethylene-induced senescence in carnation flowers

本研究以典型的乙烯依赖性衰老观赏植物康乃馨为研究对象，对其开花和衰老的分子机制进行了研究，得到以下结果：(1)利用抑制性减法杂交技术，揭示了花瓣细胞在开花过程中上调或下调的几组基因。翻译产物的推测功能分为转录、信号转导、细胞壁修饰、脂质代谢和运输等几类。此外，从开放的康乃馨花瓣中克隆了4个编码木葡聚糖转糖基化酶/水解酶的cDNA， 3个编码扩增蛋白的cDNA和1个编码蔗糖合酶的cDNA。Real-time RT-PCR分析显示，在花瓣发育（伸长、扩张和向外弯曲）过程中，这些基因的表达不同，表明这些基因在花瓣发育过程中表达受到调控。(2)首次在‘Light Pink Barbara’康乃馨基因组中发现了ACC合成酶（DcACS1）的两个基因，分别为DcACS1a和DcACS1b。它们的区别主要在于内含子的核苷酸序列。此外，我们克隆了这些基因的基因组dna，包括它们的启动子区域，并将它们引入烟草植株。在不久的将来，将有可能看到这些基因是否会诱导烟草花在衰老过程中产生更年期乙烯。(3)我们发现了一个编码富甘氨酸RNA结合蛋白（DgGRP1）的基因，其启动子中含有乙烯反应元件（ERE），在康乃馨花衰老过程中下调。该基因将在不久的将来与半胱氨酸蛋白酶1（DcCP1）基因进行比较分析，DcCP1基因在其启动子上有一个ERE，但在花衰老过程中上调。

In this research project, we have investigated the molecular mechanism of flowering and senescence of carnation flower, which is a typical ornamental showing ethylene-dependent senescence, and obtained the following results.(1) We revealed several groups of genes which are up- or down-regulated in petal cells during flower opening by a suppressive subtractive hybridization technique. The putative functions of the translational products were classified into several categories including transcription, signaling, cell wall modification, lipid metabolism, and transport. Furthermore, four cDNAs encoding xyloclucantransglucosylase/hy-drolase, three cDNAs encoding expansin and a cDNA encoding sucrose synthase were cloned from petals of opening carnation flowers. Real-time RT-PCR analyses revealed that respective genes are differently expressed during petal development (elongation, expansion and outward-bending), indicating regulated expression of these genes during this process.(2) We revealed the presence of two genes of an ACC synthase (DcACS1), designated as DcACS1a and DcACS1b in the genome of 'Light Pink Barbara' carnation for the first time. They differ mainly in the nucleotide sequences of introns. Moreover, we cloned genomic DNAs of these genes, including their promoter region, and introduced them into tobacco plants. In the near future, it will be possible to see whether these genes will induce climacteric ethylene production in tobacco flowers undergoing senescence.(3) We discovered a gene encoding glycine-rich RNA binding protein (DgGRP1), which has an ethlylene response element (ERE) in its promoter and is down-regulated during carnation flower senescence. This gene will be analyzed in the near future by comparing with cysteine proteinase 1(DcCP1) gene, which has an ERE in its promoter but up-regulated during flower senescence.