The Arabidopsis ALDP protein homologue COMATOSE is instrumental in peroxisomal acetate metabolism
Résumé
The Arabidopsis acn (acetate non-utilizing) mutants were isolated based on fluoroacetate resistant germination and seedling establishment. We report the characterization of the acn2 mutant. Physiological analyses of acn2 showed that it possessed characteristics similar to the mutants cts-1 (COMATOSE) and pxa1 (peroxisomal ABC transporter 1). The acn2 locus was mapped to within 3 cM of the COMATOSE gene on the bottom arm of chromosome IV using CAPS and SSLP markers. Crossing acn2 and cts-1 failed to restore the fluoroacetate sensitive phenotype suggesting allelism of the mutations. Sequencing of the ACN2 locus revealed a C-T nonsense mutation in exon 13, which would result in elimination of the C-terminal hemitransporter domain of the encoded protein. Neither full-length CTS protein nor truncated protein was detected on immunoblots using C-terminal or N-terminal specific anti-CTS antibodies, respectively, demonstrating the absence of the entire CTS protein in acn2. Emerged seedlings of both cts-1 and pxa1 alleles displayed increased resistance to FAc compared to corresponding wild-types. Both cts-1 and pxa1 mutant lines expressing the wild-type protein through complementation were FAc sensitive demonstrating that mutation of the COMATOSE gene was responsible for the FAc resistant phenotype. Feeding studies confirmed that both acn2 and cts-1 were compromised in their ability to convert radiolabelled acetate into soluble carbohydrates. These results demonstrate a role for the ABC protein COMATOSE in providing acetate to the glyoxylate cycle in developing seedlings.
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