Members of the tomato LeEIL (EIN3-like) gene family are functionally redundant and regulate ethylene responses throughout plant development

The plant hormone ethylene regulates many aspects of growth, development and responses to the environment. The Arabidopsis ETHYLENE INSENSITIVE3 (EIN3) protein is a nuclear-localized component of the ethylene signal-transduction pathway with DNA-binding activity. Loss-of-function mutations in this protein result in ethylene insensitivity in Arabidopsis. To gain a better understanding of the ethylene signal-transduction pathway in tomato, we have identified three homologs of the Arabidopsis EIN3 gene (LeEILs). Each of these genes complemented the ein3-1 mutation in transgenic Arabidopsis, indicating that all are involved in ethylene signal transduction. Transgenic tomato plants with reduced expression of a single LeEIL gene did not exhibit significant changes in ethylene response; reduced expression of multiple tomato LeEIL genes was necessary to reduce ethylene sensitivity significantly. Reduced LeEIL expression affected all ethylene responses examined, including leaf epinasty, flower abscission, flower senescence and fruit ripening. Our results indicate that the LeEILs are functionally redundant and positive regulators of multiple ethylene responses throughout plant development.     

Cholera toxin elevates pathogen resistance and induces pathogenesis-related gene expression in tobacco.

In animals, plants and fungi, cholera toxin (CTX) can activate signalling pathways dependent on heterotrimeric GTP binding proteins (G-proteins). We transformed tobacco plants with a chimeric gene encoding the A1 subunit of CTX regulated by a light-inducible wheat Cab-1 promoter. Tissues of transgenic plants expressing CTX showed greatly reduced susceptibility to the bacterial pathogen Pseudomonas tabaci, accumulated high levels of salicylic acid (SA) and constitutively expressed pathogenesis-related (PR) protein genes encoding PR-1 and the class II isoforms of PR-2 and PR-3. In contrast, the class I isoforms of PR-2 and PR-3 known to be induced in tobacco by stress, by ethylene treatment and as part of the hypersensitive response to infection, were not induced and displayed normal regulation. In good agreement with these results, microinjection experiments demonstrated that CTX or GTP-gamma-S induced the expression of a PR1-GUS reporter gene but not that of a GLB-GUS reporter gene containing the promoter region of a gene encoding the class I isoform of PR-2. Microinjection and grafting experiments strongly suggest that CTX-sensitive G-proteins are important in inducing the expression of a subset of PR genes and that these G-proteins act locally rather than systemically upstream of SA induction.     

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.     

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。     

Mutual regulation of Arabidopsis thaliana ethylene-responsive element binding protein and a plant floral homeotic gene, APETALA2

BACKGROUND AND AIMS: It has previously been shown that Arabidopsis thaliana ethylene-responsive element binding protein (AtEBP) contributed to resistance to abiotic stresses. Interestingly, it has also been reported that expression of ethylene-responsive factor (ERF) genes including AtEBP were regulated by the activity of APETALA2 (AP2), a floral homeotic factor. AP2 is known to regulate expression of several floral-specific homeotic genes such as AGAMOUS. The aim of this study was to clarify the relationship between AP2 and AtEBP in gene expression. METHODS: Northern blot analysis was performed on ap2 mutants, ethylene-related Arabidopsis mutants and transgenic Arabidopsis plants over-expressing AtEBP, and a T-DNA insertional mutant of AtEBP. Phenotypic analysis of these plants was performed. KEY RESULTS: Expression levels of ERF genes such as AtEBP and AtERF1 were increased in ap2 mutants. Over-expression of AtEBP caused upregulation of AP2 expression in leaves. AP2 expression was suppressed by the null-function of ethylene-insensitive2 (EIN2), although AP2 expression was not affected by ethylene treatment. Loss of AtEBP function slightly reduced the average number of stamens. CONCLUSIONS: AP2 and AtEBP are mutually regulated in terms of gene expression. AP2 expression was affected by EIN2 but was not regulated by ethylene treatment.     

高等植物EIN3/EILs转录因子研究进展

Ethylene-insensitive3(EIN3)和EIN3-like(EIL)蛋白是乙烯信号转导途径中重要的核转录因子。目前已经从多种高等植物中分离得到EIN3/EILs,其属于一个小的转录因子家族。这类转录因子在氨基酸序列N端高度保守,包括酸性氨基酸区、脯氨酸富集区、碱性氨基酸簇等涉及DNA结合的重要结构域,它们通过直接结合到初级乙烯反应元件(PERE)上来调节相关基因的表达。EIN3/EILs转录因子家族不同成员在不同物种间时空表达特性、表达调控模式等均有所差异,各成员主要参与调节植物对乙烯的反应,包括影响幼苗的"三重反应"、植株的生长发育等,并作为乙烯与其他信号间交叉点发挥重要作用。就近几年关于高等植物EIN3/EILs转录因子的研究进展进行综述,以期为后续研究提供理论依据。