SALT-SENSITIVE MUTANTS OF CHLAMYDOMONAS-REINHARDTII ISOLATED AFTER INSERTIONAL TAGGING

We describe the isolation of salt-sensitive Chlamydomonas reinhardtii mutants by insertional mutagenesis using the nitrate reductase (Nit1) gene. The plasmid pMN24, containing Nit1, was used for transformation of 305CW15 (nit1 cw15 mt(+)), and transformants were selected for comp lementation of the nit(-) phenotype. From 6875 nit(+) colonies, four t ransformants (S4, S18, S46, and S66) were isolated that exhibited both Na+ and Li+ sensitivity (sod(-)), and another transformant (S33) was selected that exhibited sensitivity to Li+ but not Na+ (lit(-)) based on relative growth comparisons with the wild-type strain. S33, S46, an d S66 were no more growth inhibited by sorbitol than was 305CW15. In c omparison, S4 and S18 exhibited substantial growth inhibition in mediu m supplemented with sorbitol. Genetic analyses indicated that the salt -sensitive mutants were each defective in a single recessive gene. The mutant genes in S4 (sod1), S33 (lit1), and S66 (sod3) are linked to a functional copy of Nit1 and are presumably tagged with a pMN24 insert ion.