THE HYBRID HISTIDINE KINASE DHKB REGULATES SPORE GERMINATION IN DICTYOSTELIUM-DISCOIDEUM

Spore germination is a defined developmental process that marks a crit ical point in the life cycle of Dictyostelium discoideum. Upon germina tion the environmental conditions must be conducive to cell growth to ensure survival of emerged amoebae. However, the signal transduction p athways 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 pr edicted to be a transmembrane hybrid sensor kinase. The dhkB-null cell s develop with normal timing to give what seem to be mature fruiting b odies by 22 to 24 h. However, over the next several hours, the ellipso idal and encapsulated spores proceed to swell and germinate in situ wi thin the sorus and thus do not respond to the normal inhibitors of ger mination present within the sorus. The emerged amoebae dehydrate due t o 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. Precocio us germination is suppressed by ectopic activation of or expression of cAMP-dependent protein kinase A. Additionally, at 24 h the intracellu lar concentration of cAMP of dhkB(-) spores is 40% that of dhkB(+) spo res. The results indicate that DHKB regulates spore germination, and a functional DHKB sensor kinase is required for the maintenance of spor e dormancy. DHKB probably acts by maintaining an active PKA that in tu rn is inhibitory to germination. (C) 1998 Academic Press.