PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan.
Department of Biological Science, Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan.
Microbiology (Reading). 2012 Jun;158(Pt 6):1437-1443. doi: 10.1099/mic.0.057729-0. Epub 2012 Mar 1.
Anabaena sp. strain PCC 7120 is a filamentous cyanobacterium in which certain vegetative cells differentiate into heterocysts, which are specialized cells for nitrogen fixation. Heterocysts are unable to carry out photosynthesis and are supplied with carbohydrate required for nitrogen fixation from neighbouring vegetative cells. Thus, filament integrity is very important for diazotrophic growth of the heterocystous cyanobacteria. The pknH gene (alr1336), encoding a putative Ser/Thr protein kinase, was upregulated in heterocysts after nitrogen deprivation. Its expression was developmentally regulated by the hetR gene. Expression levels of genes involved in heterocyst maturation, such as hepA, hglE and nifH, in the pknH disruptant were similar to those of the wild-type strain. The disruptant was able to form heterocysts with nitrogenase activity, but most heterocysts were detached from filaments. Hence, the pknH disruptant showed a growth defect in the medium without combined nitrogen. It is concluded that the pknH gene is not involved in the development of heterocyst function but is involved in maintaining connections between heterocysts and vegetative cells.
鱼腥藻 PCC 7120 是一种丝状蓝藻，其中某些营养细胞分化为异形胞，异形胞是专门进行固氮的细胞。异形胞无法进行光合作用，其固氮所需的碳水化合物由邻近的营养细胞提供。因此，丝状完整性对于异形胞固氮蓝藻的固氮生长非常重要。pknH 基因（alr1336）编码一个假定的丝氨酸/苏氨酸蛋白激酶，在氮饥饿后在异形胞中上调。其表达受 hetR 基因的发育调控。在 pknH 突变体中，参与异形胞成熟的基因如 hepA、hglE 和 nifH 的表达水平与野生型菌株相似。突变体能够形成具有固氮酶活性的异形胞，但大多数异形胞从丝状体上脱落。因此，pknH 突变体在没有组合氮的培养基中表现出生长缺陷。因此可以得出结论，pknH 基因不参与异形胞功能的发育，但参与维持异形胞和营养细胞之间的连接。
