Regulation of hydrogenase gene expression in Chlamydomonas

Xiaoqing Sun1, Susan Pribyl2, Nancy Haas1, Paul A. Lefebvre1, and Carolyn D. Silflow1

1) Department of Plant Biology, University of Minnesota, St. Paul, MN, USA 2) Dept of Genetics, Cell Biology, and Development, University of Minnesota, St. Paul, MN, USA

Under anaerobic conditions Chlamydomonas can produce hydrogen catalyzed by the two hydrogenases HYDA1 and HYDA2. The transcripts are present at low levels in aerobically grown cells but are induced under anaerobic conditions. The goals of this project are to examine the regulation of hydrogenase gene expression and to identify components in the anaerobic signaling pathway in Chlamydomonas by using a cell motility reporter gene system. Constructs containing the promoter and 5'UTR of HYDA1 or HYDA2 fused to the coding sequence of PF14 (pHYDA1::PF14 and pHYDA1::PF14) were transformed into immotile pf14 mutant cells. Transformants remained immotile in aerobic conditions but gained motility after anaerobic induction, indicating a transcriptional control of HYDA gene expression. From the conditionally swimming transformants we selected constitutively swimming mutants. Preliminary Northern results indicated elevated HYDA transcript levels in a number of mutants. Further characterization of these mutants may reveal factors involved in regulation of hydrogenase gene expression or in the anaerobic signaling pathway. A Tcr1 transposon insertion in the introduced HYDA2 promoter-5'UTR sequence in the pHYDA2::PF14 construct causes constitutive expression of the PF14 reporter gene in one mutant strain C5-4. Further analysis of this mutant will shed light on a possible enhancer function in the Tcr1 transposon or on cis-regulating factors of the HYDA2 gene.

e-mail address of presenting author: sunxx125@umn.edu