Zinda M J, Singleton C K
Department of Molecular Biology, Vanderbilt University, Nashville, Tennessee 37235, USA.
Dev Biol. 1998 Apr 15;196(2):171-83. doi: 10.1006/dbio.1998.8854.
Spore germination is a defined developmental process that marks a critical point in the life cycle of Dictyostelium discoideum. Upon germination the environmental conditions must be conducive to cell growth to ensure survival of emerged amoebae. However, the signal transduction pathways controlling the various aspects of spore germination in large part remain to be elucidated. We have used degenerate PCR to identify dhkB, a two-component histidine kinase, from D. discoideum. DhkB is predicted to be a transmembrane hybrid sensor kinase. The dhkB-null cells develop with normal timing to give what seem to be mature fruiting bodies by 22 to 24 h. However, over the next several hours, the ellipsoidal and encapsulated spores proceed to swell and germinate in situ within the sorus and thus do not respond to the normal inhibitors of germination present within the sorus. The emerged amoebae dehydrate due to the high osmolarity within the sorus, and by 72 h 4% or less of the amoebae remain as spores, while most cells are now nonviable. Precocious germination is suppressed by ectopic activation of or expression of cAMP-dependent protein kinase A. Additionally, at 24 h the intracellular concentration of cAMP of dhkB- spores is 40% that of dhkB+ spores. The results indicate that DHKB regulates spore germination, and a functional DHKB sensor kinase is required for the maintenance of spore dormancy. DHKB probably acts by maintaining an active PKA that in turn is inhibitory to germination.
孢子萌发是一种特定的发育过程，标志着盘基网柄菌生命周期中的一个关键点。萌发时，环境条件必须有利于细胞生长，以确保新出现的变形虫能够存活。然而，在很大程度上，控制孢子萌发各个方面的信号转导途径仍有待阐明。我们利用简并PCR从盘基网柄菌中鉴定出双组分组氨酸激酶dhkB。预测DhkB是一种跨膜杂交传感器激酶。缺失dhkB的细胞正常发育，在22至24小时时形成看似成熟的子实体。然而，在接下来的几个小时里，椭圆形且被包裹的孢子在孢子果内原位膨胀并萌发，因此对孢子果内正常的萌发抑制剂没有反应。由于孢子果内的高渗透压，新出现的变形虫脱水，到72小时时，只有4%或更少的变形虫仍以孢子形式存在，而大多数细胞此时已无活力。异位激活或表达cAMP依赖性蛋白激酶A可抑制早熟萌发。此外，在24小时时，缺失dhkB的孢子的细胞内cAMP浓度是含有dhkB的孢子的40%。结果表明，DHKB调节孢子萌发，功能性的DHKB传感器激酶是维持孢子休眠所必需的。DHKB可能通过维持一种活跃的PKA起作用，而PKA反过来又抑制萌发。
