Resistance to l -methionine-S-sulfoximine in Chlamydomonas reinhardtii is due to an alteration in a general amino acid transport system

Abstract

It was suggested that the mutant ARF1 of Chlamydomonas reinhardtii is resistant to L-methionine-S-sulfoximine (MSX, an irreversible inhibitor of glutamine synthetase, EC 6.3.1.2) because this strain degraded and utilized this compound as a nitrogen source for growth (A.R. Franco et al., 1996. Resistance to MSX has now been characterized in a double mutant of this alga, called MPA1, which is resistant to MSX and lacks L-amino acid oxidase (LAO activity, EC 1.4.3.2). Biochemical and genetic evidence indicate that the mutant MPA1 is altered in the same MSX-resistance locus as mutant ARF1. However, mutant MPA1 neither degraded nor utilized MSX as a nitrogen source. This led us to conclude that (i) resistance to MSX is not linked to its utilization, and (ii) that LAO activity accounts for the degradation of MSX in mutant ARF1. Data indicate that C. reinhardtii possesses a broad-speci®city carrier system responsible for the transport of arginine and other amino acids, including MSX. We propose that the alteration of this carrier confers resistance to MSX in mutants ARF1 and MPA1.This work is dedicated to the memory of Professor J. Ca rdenas Abbreviations: GS Glutamine synthase; LAO L-amino acid oxidase; MKAT MSX/a-ketoglutarate amino transferase; MSX L-methionine-S-sulfoximine; mt mating type; PPT phosphinothricin; PPO 4-methyl phosphinico-2-oxobutanoic acid; TAP Tris-acetate-phosphate

RNA-Seq Analysis of Sulfur-Deprived Chlamydomonas Cells Reveals Aspects of Acclimation Critical for Cell Survival

“…An increase in the AOT4 transcript level did not occur in phosphorous-depleted (2P) or nitrogen-depleted (2N) cells ( Figure 6A). Although the only amino acid-specific transport activity that has been demonstrated in Chlamydomonas is for Arg (Kirk and Kirk, 1978), the existence of additional amino acid transporters has been proposed (Perez-Alegre and Franco, 1998), and recently we demonstrated that wild-type Chlamydomonas cells, unlike the snrk2.1 mutant, were able to grow slowly The log 2 relative expression values of 1.5 and À1.5 were selected as the thresholds to designate the categories of transcripts that accumulate (or are more abundant) and decline (or are less abundant), respectively, for wild type -S/wild type +S (I) and snrk2.1 -S/wild type -S (II) conditions. For more details about each of the categories, see Methods.…”

Distribution in Different Organisms of Amino Acid Oxidases with FAD or a Quinone As Cofactor and Their Role as Antimicrobial Proteins in Marine Bacteria

“…It is proposed that the utilization of amino acids as nitrogen source is their major physiological function. This role is also assumed for LAAOs in other eukaryotic microorganisms such as the single-cell alga Chlamydomonas reinhardtii [ 64 , 65 ]. Accordingly, fungal LAAOs usually have a broad substrate range to be able to use distinct amino acids for growing.…”