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First published online September 23, 2005; 10.1104/pp.105.065037 Plant Physiology 139:999-1014 (2005) © 2005 American Society of Plant Biologists Mating-Induced Shedding of Cell Walls, Removal of Walls from Vegetative Cells, and Osmotic Stress Induce Presumed Cell Wall Genes in Chlamydomonas1Institute of Biology III, Albert-Ludwigs-University, D79104 Freiburg, Germany
The first step in sexual differentiation of the unicellular green alga Chlamydomonas reinhardtii is the formation of gametes. Three genes, GAS28, GAS30, and GAS31, encoding Hyp-rich glycoproteins that presumably are cell wall constituents, are expressed in the late phase of gametogenesis. These genes, in addition, are activated by zygote formation and cell wall removal and by the application of osmotic stress. The induction by zygote formation could be traced to cell wall shedding prior to gamete fusion since it was seen in mutants defective in cell fusion. However, it was absent in mutants defective in the initial steps of mating, i.e. in flagellar agglutination and in accumulation of adenosine 3',5'-cyclic monophosphate in response to this agglutination. Induction of the three GAS genes was also observed when cultures were exposed to hypoosmotic or hyperosmotic stress. To address the question whether the induction seen upon cell wall removal from both gametes and vegetative cells was elicited by osmotic stress, cell wall removal was performed under isosmotic conditions. Also under such conditions an activation of the genes was observed, suggesting that the signaling pathway(s) is (are) activated by wall removal itself.
1 This work was supported by a grant from the Deutsche Forschungsgemeinschaft to C.F.B. X.-K.H. acknowledges the support by the Deutscher Akademischer Austauschdienst for a stay in the laboratory of Dr. Purton. Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.065037. * Corresponding author; e-mail beck{at}uni-freiburg.de; fax 497612032745. Received May 10, 2005; returned for revision July 5, 2005; accepted July 15, 2005. Related articles in Plant Physiol.:
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