Department of Biochemistry, University of California, Riverside, CA 92521-0129, USA.
Plant Mol Biol. 2010 Nov;74(4-5):405-21. doi: 10.1007/s11103-010-9686-4. Epub 2010 Sep 12.
Ethylene, a regulator of plant growth and development, is perceived by specific receptors that act as negative regulators of the ethylene response. Five ethylene receptors, i.e., ETR1, ERS1, EIN4, ETR2, and ERS2, are present in Arabidopsis and dominant negative mutants of each that confer ethylene insensitivity have been reported. In contrast, maize contains just two types of ethylene receptors: ZmERS1, encoded by ZmERS1a and ZmERS1b, and ZmETR2, encoded by ZmETR2a and ZmETR2b. In this study, we introduced a Cys to Tyr mutation in the transmembrane domain of ZmERS1b and ZmETR2b that is present in the etr1-1 dominant negative mutant and expressed each protein in Arabidopsis. Mutant Zmers1b and Zmetr2b receptors conferred ethylene insensitivity and Arabidopsis expressing Zmers1b or Zmetr2b were larger and exhibited a delay in leaf senescence characteristic of ethylene insensitive Arabidopsis mutants. Zmers1b and Zmetr2b were dominant and functioned equally well in a hemizygous or homozygous state. Expression of the Zmers1b N-terminal transmembrane domain was sufficient to exert dominance over endogenous Arabidopsis ethylene receptors whereas the Zmetr2b N-terminal domain failed to do so. Neither Zmers1b nor Zmetr2b functioned in the absence of subfamily 1 ethylene receptors, i.e., ETR1 and ERS1. These results suggest that Cys65 in maize ZmERS1b and ZmETR2b plays the same role that it does in Arabidopsis receptors. Moreover, the results demonstrate that the mutant maize ethylene receptors are functionally dependent on subfamily 1 ethylene receptors in Arabidopsis, indicating substantial functional conservation between maize and Arabidopsis ethylene receptors despite their sequence divergence.
乙烯作为一种植物生长和发育的调节剂，被特定的受体感知，这些受体作为乙烯反应的负调节剂发挥作用。拟南芥中存在 5 种乙烯受体，即 ETR1、ERS1、EIN4、ETR2 和 ERS2，并且已经报道了每个受体的显性负突变体，这些突变体赋予了对乙烯的不敏感性。相比之下，玉米只含有两种类型的乙烯受体：ZmERS1，由 ZmERS1a 和 ZmERS1b 编码，以及 ZmETR2，由 ZmETR2a 和 ZmETR2b 编码。在这项研究中，我们在 ZmERS1b 和 ZmETR2b 的跨膜结构域中引入了一个 Cys 到 Tyr 的突变，这个突变存在于 etr1-1 显性负突变体中，并在拟南芥中表达了每种蛋白。突变体 Zmers1b 和 Zmetr2b 赋予了对乙烯的不敏感性，并且表达 Zmers1b 或 Zmetr2b 的拟南芥更大，并且表现出与乙烯不敏感的拟南芥突变体相似的叶片衰老延迟。Zmers1b 和 Zmetr2b 是显性的，在半合子或纯合子状态下功能相同。Zmers1b 的 N 端跨膜结构域的表达足以对拟南芥内源乙烯受体发挥显性作用，而 Zmetr2b 的 N 端结构域则不能。Zmers1b 和 Zmetr2b 在缺乏亚家族 1 乙烯受体（即 ETR1 和 ERS1）的情况下均不起作用。这些结果表明，玉米 ZmERS1b 和 ZmETR2b 中的 Cys65 发挥着与拟南芥受体相同的作用。此外，这些结果表明，突变的玉米乙烯受体在拟南芥中依赖于亚家族 1 乙烯受体，这表明尽管玉米和拟南芥乙烯受体的序列存在差异，但它们的功能仍然具有很大的保守性。
