Kim Hyo Jung, Ryu Hojin, Hong Sung Hyun, Woo Hye Ryun, Lim Pyung Ok, Lee In Chul, Sheen Jen, Nam Hong Gil, Hwang Ildoo
Division of Molecular and Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea.
Proc Natl Acad Sci U S A. 2006 Jan 17;103(3):814-9. doi: 10.1073/pnas.0505150103. Epub 2006 Jan 9.
Cytokinins are plant hormones with profound roles in growth and development, including control of leaf longevity. Although the cytokinin signal is known to be perceived by histidine kinase receptors, the underlying molecular mechanism and specificity of the receptors leading to delayed leaf senescence have not yet been elucidated. Here, we found that AHK3, one of the three cytokinin receptors in Arabidopsis, plays a major role in controlling cytokinin-mediated leaf longevity through a specific phosphorylation of a response regulator, ARR2. This result was obtained through identification of a gain-of-function Arabidopsis mutant that shows delayed leaf senescence because of a missense mutation in the extracellular domain of AHK3. A loss-of-function mutation in AHK3, but not of the other cytokinin receptors, conferred a reduced sensitivity to cytokinin in cytokinin-dependent delay of leaf senescence and abolished cytokinin-dependent phosphorylation of ARR2. Consistently, transgenic overexpression of wild-type, but not an unphosphorylatable mutant ARR2, led to delayed senescence of leaves.
细胞分裂素是一类在植物生长发育过程中具有重要作用的植物激素，包括对叶片寿命的调控。虽然已知细胞分裂素信号是由组氨酸激酶受体感知的，但导致叶片衰老延迟的受体潜在分子机制和特异性尚未阐明。在此，我们发现拟南芥三种细胞分裂素受体之一的AHK3，通过对响应调节因子ARR2的特异性磷酸化作用，在控制细胞分裂素介导的叶片寿命中起主要作用。这一结果是通过鉴定一个功能获得型拟南芥突变体得到的，该突变体由于AHK3胞外域的错义突变而表现出叶片衰老延迟。AHK3的功能缺失突变，而非其他细胞分裂素受体的功能缺失突变，在细胞分裂素依赖的叶片衰老延迟中赋予了对细胞分裂素的敏感性降低，并消除了细胞分裂素依赖的ARR2磷酸化。同样，野生型而非不可磷酸化的突变体ARR2的转基因过表达导致了叶片衰老延迟。
