Adenylyl Cyclase G, an Osmosensor Controlling Germination of Dictyostelium Spores

doi:10.1074/jbc.271.39.23623

Adenylyl Cyclase G, an Osmosensor Controlling Germination of Dictyostelium Spores*

From the ^‡ Cell Biology Section, Institute for Molecular Plant Sciences, University of Leiden, Wassenaarseweg 64, 2333AL Leiden, The Netherlands, the
^§Department of Biological Sciences, University of Windsor, Windsor, Ontario N9B3P4, Canada, and the
^¶Department of Biological Chemistry, The Johns Hopkins University Medical School, Baltimore, Maryland 21205

^∥To whom correspondence should be addressed:
Cell Biology Section, Inst. for Molecular Plant Sciences, University of Leiden, Wassenaarseweg 64, 2333AL Leiden, The Netherlands.
Tel.: 31-71-5274927; Fax: 31-71-5274999.

Abstract

Dictyostelium cells express a G-protein-coupled adenylyl cyclase, ACA, during aggregation and an atypical adenylyl cyclase, ACG, in mature spores. The ACG gene was disrupted by homologous recombination. acg⁻ cells developed into normal fruiting bodies with viable spores, but spore germination was no longer inhibited by high osmolarity, a fairly universal constraint for spore and seed germination. ACG activity, measured in aca⁻/ACG cells, was strongly stimulated by high osmolarity with optimal stimulation occurring at 200 milliosmolar. RdeC mutants, which display unrestrained protein kinase A (PKA) activity and a cell line, which overexpresses PKA under a prespore specific promoter, germinate very poorly, both at high and low osmolarity. These data indicate that ACG is an osmosensor controlling spore germination through activation of protein kinase A.

Footnotes

↵* This research was supported by Grant 805.17.046 from the Life Sciences Foundation of the Netherlands Organization for Scientific Research and by a travel grant from the Netherlands Organization for Scientific Research. The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

ACA

aggregation adenylyl cyclase

ACG

germination adenylyl cyclase

Rde

rapid developing

PKA

cAMP-dependent protein kinase

DTT

dithiothreitol

NEO^R

Tn5 aminoglycoside phosphotransferase

PDE

cAMP phosphodiesterase.
- Received March 22, 1996.
- Revision received August 1, 1996.