Hackett R M, Ho C W, Lin Z, Foote H C, Fray R G, Grierson D
Plant Science Division, School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough LE12 5RD, United Kingdom.
Plant Physiol. 2000 Nov;124(3):1079-86. doi: 10.1104/pp.124.3.1079.
The hormone ethylene regulates many aspects of plant growth and development, including fruit ripening. In transgenic tomato (Lycopersicon esculentum) plants, antisense inhibition of ethylene biosynthetic genes results in inhibited or delayed ripening. The dominant tomato mutant, Never-ripe (Nr), is insensitive to ethylene and fruit fail to ripen. The Nr phenotype results from mutation of the ethylene receptor encoded by the NR gene, such that it can no longer bind the hormone. NR has homology to the Arabidopsis ethylene receptors. Studies on ethylene perception in Arabidopsis have demonstrated that receptors operate by a "receptor inhibition" mode of action, in which they actively repress ethylene responses in the absence of the hormone, and are inactive when bound to ethylene. In ripening tomato fruit, expression of NR is highly regulated, increasing in expression at the onset of ripening, coincident with increased ethylene production. This expression suggests a requirement for the NR gene product during the ripening process, and implies that ethylene signaling via the tomato NR receptor might not operate by receptor inhibition. We used antisense inhibition to investigate the role of NR in ripening tomato fruit and determine its mode of action. We demonstrate restoration of normal ripening in Nr fruit by inhibition of the mutant Nr gene, indicating that this receptor is not required for normal ripening, and confirming receptor inhibition as the mode of action of the NR protein.
激素乙烯调节植物生长和发育的许多方面，包括果实成熟。在转基因番茄（Lycopersicon esculentum）植株中，对乙烯生物合成基因的反义抑制导致成熟受到抑制或延迟。显性番茄突变体“永不成熟”（Nr）对乙烯不敏感，果实无法成熟。Nr表型是由NR基因编码的乙烯受体发生突变所致，致使其不能再与该激素结合。NR与拟南芥乙烯受体具有同源性。对拟南芥中乙烯感知的研究表明，受体通过“受体抑制”作用模式发挥功能，即在没有激素的情况下它们会积极抑制乙烯反应，而与乙烯结合时则无活性。在成熟的番茄果实中，NR的表达受到高度调控，在成熟开始时表达增加，这与乙烯产量增加同时发生。这种表达表明在成熟过程中需要NR基因产物，并且意味着通过番茄NR受体的乙烯信号传导可能不是通过受体抑制来起作用的。我们使用反义抑制来研究NR在成熟番茄果实中的作用并确定其作用模式。我们通过抑制突变的Nr基因证明了Nr果实恢复了正常成熟，这表明正常成熟不需要这种受体，并证实了受体抑制是NR蛋白的作用模式。
