A mutation in the LPAT1 gene suppresses the sensitivity of fab1 plants to low temperature

The Arabidopsis (Arabidopsis thaliana) fatty acid biosynthesis1 (fab1) mutant grows as well as wild type at 22 degrees C, but after transfer to 2 degrees C fab1 plants cannot maintain photosynthetic function and die after 5 to 7 weeks at 2 degrees C. A fab1 suppressor line, S7, was isolated in a screen that identified mutants that remained alive after 16 weeks at 2 degrees C and were able to flower and produce seed after return to 22 degrees C. Relative to wild type, S7 plants had reduced levels of 16:3 fatty acid in leaf galactolipids, indicating reduced synthesis of chloroplast glycerolipids by the prokaryotic pathway of lipid metabolism. The suppressor mutation was identified, by map-based and candidate-gene approaches, as a hypomorphic allele of lysophosphatidic acid acyltransferase1 (lpat1), lpat1-3. LPAT1 encodes the enzyme that catalyzes the second reaction in the prokaryotic pathway. Several lines of evidence indicate that damage and death of fab1 plants at 2 degrees C may be a result of the increased proportion of phosphatidylglycerol (PG) in fab1 that are high-melting-point molecular species (containing only 16:0, 18:0, and 16:1,Delta3-trans fatty acids). Consistent with this proposal, the lpat1-3 mutation strongly affects the fatty acid composition of PG. The proportion of high-melting-point molecular species in PG is reduced from 48.2% in fab1 to 10.7% in fab1 lpat1-3 (S7), a value close to the 7.6% found in wild type.