Horticultural Sciences, University of Florida, Gainesville, Florida 32611-0690, USA.
Plant Physiol. 2012 Sep;160(1):488-97. doi: 10.1104/pp.112.202820. Epub 2012 Jul 13.
Perception of the plant hormone ethylene is essential to initiate and advance ripening of climacteric fruits. Since ethylene receptors negatively regulate signaling, the suppression is canceled upon ethylene binding, permitting responses including fruit ripening. Although receptors have autophosphorylation activity, the mechanism whereby signal transduction occurs has not been fully determined. Here we demonstrate that LeETR4, a critical receptor for tomato (Solanum lycopersicum) fruit ripening, is multiply phosphorylated in vivo and the phosphorylation level is dependent on ripening stage and ethylene action. Treatment of preclimacteric fruits with ethylene resulted in accumulation of LeETR4 with reduced phosphorylation whereas treatments of ripening fruits with ethylene antagonists, 1-methylcyclopropene and 2,5-norbornadiene, induced accumulation of the phosphorylated isotypes. A similar phosphorylation pattern was also observed for Never ripe, another ripening-related receptor. Alteration in the phosphorylation state of receptors is likely to be an initial response upon ethylene binding since treatments with ethylene and 1-methylcyclopropene rapidly influenced the LeETR4 phosphorylation state rather than protein abundance. The LeETR4 phosphorylation state closely paralleled ripening progress, suggesting that the phosphorylation state of receptors is implicated in ethylene signal output in tomato fruits. We provide insights into the nature of receptor on and off states.
植物激素乙烯的感知对于启动和促进跃变型果实的成熟至关重要。由于乙烯受体负调控信号，因此在乙烯结合后会取消抑制，从而允许包括果实成熟在内的反应发生。尽管受体具有自动磷酸化活性，但信号转导发生的机制尚未完全确定。在这里，我们证明了 LeETR4 是番茄（Solanum lycopersicum）果实成熟的关键受体，它在体内被多次磷酸化，并且磷酸化水平取决于成熟阶段和乙烯的作用。乙烯处理未成熟的果实会导致 LeETR4 积累，磷酸化水平降低，而乙烯拮抗剂 1-甲基环丙烯和 2,5-降冰片二烯处理成熟果实会诱导磷酸化同工型的积累。另一个与成熟相关的受体 Never ripe 也观察到了类似的磷酸化模式。受体磷酸化状态的改变可能是乙烯结合后的初始反应，因为乙烯和 1-甲基环丙烯的处理迅速影响了 LeETR4 的磷酸化状态，而不是蛋白质丰度。LeETR4 的磷酸化状态与成熟进程密切相关，这表明受体的磷酸化状态与番茄果实中的乙烯信号输出有关。我们提供了对受体开启和关闭状态本质的深入了解。
