Co-suppression of the <Emphasis Type="Italic">EIN2</Emphasis>-homology gene <Emphasis Type="Italic">LeEIN2</Emphasis> inhibits fruit ripening and reduces ethylene sensitivity in tomato

EIN2 (ethylene insensitive 2) is a very important component in the ethylene signal transduction pathway. Recently, the genomic DNA and full-length cDNA of LeEIN2 (tomato EIN2) have been isolated in our laboratory. To reveal the function of LeEIN2, transgenic tomato plants with reduced expression levels of LeEIN2 were produced. The fruit ripening and expressions of ripening-related genes encoding polygalacturonase and TomLoxB were inhibited in the LeEIN2-silenced transgenic plants compared to the wild-type Ailsa Craig. In the seedling ethylene response assay, the transgenic tomato plants with reduced LeEIN2 expression exhibited ethylene insensitivity. These results indicate that LeEIN2 plays a critical role in regulating tomato fruit ripening and is a positive regulator in ethylene signal transduction pathway.     

RNA interference-based gene silencing as an efficient tool for functional genomics in hexaploid bread wheat

Insertional mutagenesis and gene silencing are efficient tools for the determination of gene function. In contrast to gain- or loss-of-function approaches, RNA interference (RNAi)-induced gene silencing can possibly silence multigene families and homoeologous genes in polyploids. This is of great importance for functional studies in hexaploid wheat (Triticum aestivum), where most of the genes are present in at least three homoeologous copies and conventional insertional mutagenesis is not effective. We have introduced into bread wheat double-stranded RNA-expressing constructs containing fragments of genes encoding Phytoene Desaturase (PDS) or the signal transducer of ethylene, Ethylene Insensitive 2 (EIN2). Transformed plants showed phenotypic changes that were stably inherited over at least two generations. These changes were very similar to mutant phenotypes of the two genes in diploid model plants. Quantitative real-time polymerase chain reaction revealed a good correlation between decreasing mRNA levels and increasingly severe phenotypes. RNAi silencing had the same quantitative effect on all three homoeologous genes. The most severe phenotypes were observed in homozygous plants that showed the strongest mRNA reduction and, interestingly, produced around 2-fold the amount of small RNAs compared to heterozygous plants. This suggests that the effect of RNAi in hexaploid wheat is gene-dosage dependent. Wheat seedlings with low mRNA levels for EIN2 were ethylene insensitive. Thus, EIN2 is a positive regulator of the ethylene-signaling pathway in wheat, very similar to its homologs in Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa). Our data show that RNAi results in stably inherited phenotypes and therefore represents an efficient tool for functional genomic studies in polyploid wheat.     

Ethylene captures a metal! Metal ions are involved in ethylene perception and signal transduction

More than three decades ago, transition metal such as copper or zinc were postulated to be required for the ethylene perception. However, there was no direct evidence for this metal requirement until very recently. Two studies using Arabidopsis thaliana, one genetic and the other biochemical, have provided complementary evidence for the role of copper in ethylene perception, closing this argument. Additional evidence for the importance of the metal in the ethylene-signaling pathway came with the recent discovery that EIN2, a central signal transducer in the ethylene-signaling pathway, has significant homology to the Nramp divalent cation transporters. These studies suggest that metal metabolism may have a critical role not only in ethylene perception but also in ethylene signaling.     

The central role of PhEIN2 in ethylene responses throughout plant development in petunia

The plant hormone ethylene regulates many aspects of growth and development. Loss-of-function mutations in ETHYLENE INSENSITIVE2 (EIN2) result in ethylene insensitivity in Arabidopsis, indicating an essential role of EIN2 in ethylene signaling. However, little is known about the role of EIN2 in species other than Arabidopsis. To gain a better understanding of EIN2, a petunia (Petunia x hybrida cv Mitchell Diploid [MD]) homolog of the Arabidopsis EIN2 gene (PhEIN2) was isolated, and the role of PhEIN2 was analyzed in a wide range of plant responses to ethylene, many that do not occur in Arabidopsis. PhEIN2 mRNA was present at varying levels in tissues examined, and the PhEIN2 expression decreased after ethylene treatment in petals. These results indicate that expression of PhEIN2 mRNA is spatially and temporally regulated in petunia during plant development. Transgenic petunia plants with reduced PhEIN2 expression were compared to wild-type MD and ethylene-insensitive petunia plants expressing the Arabidopsis etr1-1 gene for several physiological processes. Both PhEIN2 and etr1-1 transgenic plants exhibited significant delays in flower senescence and fruit ripening, inhibited adventitious root and seedling root hair formation, premature death, and increased hypocotyl length in seedling ethylene response assays compared to MD. Moderate or strong levels of reduction in ethylene sensitivity were achieved with expression of both etr1-1 and PhEIN2 transgenes, as measured by downstream expression of PhEIL1. These results demonstrate that PhEIN2 mediates ethylene signals in a wide range of physiological processes and also indicate the central role of EIN2 in ethylene signal transduction.     

Cloning of a cDNA encoding an ETR2-like protein (Os-ERL1) from deep water rice (Oryza sativa L.) and increase in its mRNA level by submergence, ethylene, and gibberellin treatments

A cDNA from deep water rice treated with ethylene, encoding an ethylene receptor homologous to Arabidopsis thaliana ETR2 and EIN4, was isolated using differential display and RACE techniques. The cDNA (2880 bp), corresponding to the Os-ERL1 gene (Oryza sativa ETHYLENE RESPONSE 2 like 1; GenBank accession number AB107219), contained an open reading frame of 2289 bp coding for 763 amino acids. The protein Os-ERL1 has 50% and 52% similarity to Arabidopsis ETR2 and EIN4, respectively. The Os-ERL1 gene was up-regulated by flooding, and by treatment with ethylene and gibberellin. These results suggest that deep water rice responds to flooding by increasing the number of its ethylene receptors.     

植物SAR和ISR中的乙烯信号转导网络

乙烯作为重要的信号分子在植物SAR和ISR中发挥重要作用。受病原物和其它激发子处理后,植物体内乙烯被合成,为内质网上一个His激酶类受体家族(Ⅰ型和Ⅱ型)所感知,在铜离子的转运活性下,乙烯与受体的结合使Raf-类Ser/Thr激酶CTR1失活。在CTR1的下游,EIN2、EIN3、EIN5/AIN1、EIN6、EIN7是乙烯反应的正调节子,负责乙烯信号的传导。EIN2编码功能未知的新的膜整合蛋白,而EIN5/AIN1、EIN6和EIN7尚未从分子水平上进行鉴定。定位在核内的DNA结合蛋白EIN3,直接作用于ERF1,调节乙烯反应基因的转录,激活植物防御素和病程相关蛋白基因的表达,使植物建立抗病性反应。     

水稻bicoid反义基因转基因植株胚胎发育的形态变化

Bicoid 是调控果蝇胚胎极性及以后分节发生过程的重要基因,这一基因编码的蛋白是一种转录调控因子,对一组早期胚胎发育过程中的多齿基因的表达具有调控作用,并被称为形态发生剂。在以前的工作中,从水稻cDNA文库中分离了一个同果蝇bicoid 有相当同源性的克隆—Rb24 基因（EMBL登录号：AJ2771380） 。为进一步了解它在水稻中功能,将Rb 的反义基因片段通过农杆菌的介导转入水稻中。通过Gus活性检测和PCR鉴定所获的抗性植株为转基因植株,转基因植株一个很明显的变化就是大约有50%的种子是败育的。通过石蜡切片观察了转基因水稻幼胚的发育情况,结果表明细胞和组织的分化在胚的发育过程中被阻断了。因此Rb基因同控制水稻胚的发育有关。     

水稻体内的乙烯信号传导途径(综述)

迄今为止,水稻中已经鉴定的有关乙烯信号传导途径中的组分包括乙烯受体、EIN2和EIN3的同系物,CTR1、RTE1、EBF1/2和EIN5的同系物,这些组分在双子叶植物拟南芥和单子叶植物水稻中相对保守。然而,对水稻ein2和eil1突变体的研究发现,两突变体与野生型相比并没有明显的表型差异。由此可以推断,水稻中的乙烯信号可能比拟南芥中的更加复杂。水稻依靠乙烯调节生长发育的许多方面（如对低氧环境的适应）,这些在拟南芥中是不存在的,这表明水稻可能在乙烯信号传导途径中存在新的组分或新的机制。文章就水稻体内乙烯信号传导途径、乙烯信号调节以及乙烯在水稻中的应答进行综述。