Production and characterization of an insertion mutant of Chlamydomonas reinhardtii with impaired chemotaxis towards sucrose

Motile cells of the unicellular green alga Chlamydomonas reinhardtii manife st chemotaxis towards sucrose, maltose, xylose, and mannitol. To obtain mut ants with impaired chemotaxis towards sucrose, we used the method of random insertional mutagenesis. Strain cw15arg7 was transformed with a pARG7.8 pl asmid that carried the gene of C. reinhardtii argininosuccinate lyase. Out of 68 transformants screened for chemotaxis, strain TF1, which had complete ly lost chemotaxis towards sucrose but maintained the normal reaction towar ds other attractants, was selected. The total DNA isolated from the TF1 mut ant was analyzed using Southern molecular hybridization. Tetrad analysis of crosses between TF1 and the initial strain demonstrated that the loss of c hemotaxis towards sucrose resulted from the integration of the pARG7.8 plas mid into the nuclear gene controlling chemotaxis towards sucrose. Thus, nuc lear transformation was shown to produce chemotactic C. reinhardtii mutants .