Pischke Melissa S, Jones Linda G, Otsuga Denichiro, Fernandez Donna E, Drews Gary N, Sussman Michael R
Biotechnology Center, University of Wisconsin, 425 Henry Mall, Madison 53706, USA.
Proc Natl Acad Sci U S A. 2002 Nov 26;99(24):15800-5. doi: 10.1073/pnas.232580499. Epub 2002 Nov 8.
Cytokinin-Independent 1 (CKI1) belongs to a group of putative plant histidine kinases whose members do not appear to act as ethylene receptors. The deduced protein structure, combined with the observation that Arabidopsis callus cultures overexpressing CKI1 exhibit a "cytokinin-independent" cell division and greening phenotype, led to the hypothesis that CKI1 is involved in cytokinin signaling, perhaps acting as a cytokinin receptor. To test the function of CKI1, we used a reverse-genetic approach to identify plants carrying T-DNA insertions in CKI1. Two independent alleles were identified, which produce the same developmental phenotype. Analyses of populations segregating for the cki1-5 or cki1-6 T-DNA insertion alleles failed to reveal any homozygous cki1 plants, indicating that the homozygous mutant condition was lethal. Based on segregation distortion, transmission studies, a microscopy-based examination of developing female gametophytes, and mRNA expression data, we suggest that CKI1 function is required for megagametophyte development. Our work with CKI1 mutants indicates that signal transduction by means of a HisAsp phosphorelay system may play an important and previously unsuspected role in female gametophyte development in Arabidopsis.
细胞分裂素非依赖型1（CKI1）属于一类假定的植物组氨酸激酶，其成员似乎并非作为乙烯受体发挥作用。推导的蛋白质结构，再加上对过表达CKI1的拟南芥愈伤组织培养物表现出“细胞分裂素非依赖型”细胞分裂和绿化表型的观察，引出了CKI1参与细胞分裂素信号传导、可能作为细胞分裂素受体发挥作用的假说。为了测试CKI1的功能，我们采用反向遗传学方法来鉴定在CKI1中携带T-DNA插入的植物。鉴定出了两个独立的等位基因，它们产生相同的发育表型。对cki1-5或cki1-6 T-DNA插入等位基因分离群体的分析未能发现任何纯合cki1植物，这表明纯合突变体状态是致死的。基于分离畸变、遗传传递研究、对发育中的雌配子体进行的显微镜检查以及mRNA表达数据，我们认为大孢子体发育需要CKI1发挥功能。我们对CKI1突变体的研究表明，通过组氨酸-天冬氨酸磷酸化中继系统进行的信号转导可能在拟南芥雌配子体发育中发挥重要且此前未被怀疑过的作用。
