Yonekura-Sakakibara Keiko, Kojima Mikiko, Yamaya Tomoyuki, Sakakibara Hitoshi
Plant Science Center, RIKEN, 1-7-22, Suehiro, Tsurumi, Yokohama 230-0045, Japan.
Plant Physiol. 2004 Apr;134(4):1654-61. doi: 10.1104/pp.103.037176. Epub 2004 Apr 2.
Genes for cytokinin-responsive His-protein kinases (ZmHK1, ZmHK2, and ZmHK3a) were isolated from maize (Zea mays). Heterologous expression of each of the ZmHKs in Escherichia coli having the DeltarcsC and cpslacZ genetic background conferred cytokinin-inducibility of lacZ expression on the bacteria. In the recombinant E. coli system, ZmHK1 and ZmHK3a were more sensitive to free-base cytokinins than to the corresponding nucleosides; isopentenyladenine was most effective for ZmHK1, while ZmHK2 tended to be most sensitive to trans-zeatin and the riboside. In contrast to a known cytokinin receptor of Arabidopsis (AHK4/CRE1/WOL), all ZmHKs responded to cis-zeatin (cZ), which generally is believed to be inactive or only weakly active. In cultured maize cells, expression of ZmRR1, a cytokinin-inducible response regulator, was induced by cZ as well as by trans-zeatin. These results strongly suggest that maize cytokinin receptors differ in ligand preference, and that cZ is an active cytokinin at least in maize.
从玉米（Zea mays）中分离出了细胞分裂素应答组氨酸蛋白激酶（ZmHK1、ZmHK2和ZmHK3a）的基因。在具有DeltarcsC和cpslacZ遗传背景的大肠杆菌中对每个ZmHK进行异源表达，可使细菌中lacZ表达具有细胞分裂素诱导性。在重组大肠杆菌系统中，ZmHK1和ZmHK3a对游离碱细胞分裂素比相应的核苷更敏感；异戊烯腺嘌呤对ZmHK1最有效，而ZmHK2往往对反式玉米素及其核苷最敏感。与已知的拟南芥细胞分裂素受体（AHK4/CRE1/WOL）不同，所有ZmHKs都对顺式玉米素（cZ）有反应，而cZ通常被认为是无活性的或只有微弱活性。在培养的玉米细胞中，细胞分裂素诱导型反应调节因子ZmRR1的表达可被cZ以及反式玉米素诱导。这些结果有力地表明，玉米细胞分裂素受体在配体偏好上存在差异，并且cZ至少在玉米中是一种活性细胞分裂素。
