Novel mutations affecting leaf stearate content and plant size in Arabidopsis

The fab2-1 mutant of Arabidopsis is an extreme dwarf as a direct result of an increase in the levels of stearate (18:0) in membrane lipids. We isolated a series of lines in which second-site suppressor mutations partly alleviate the dwarf phenotype. In all four of the suppressor lines examined, restoration of more normal morphology is accompanied by decreases in leaf 18:0 content. Three of the isolated suppressors suppress the high stearate phenotype in both leaves and seeds. The effects of one of the suppressors, TW2-1, is limited to the leaves. A second allele at the fab2 locus, fab2-2, was also identified and plants homozygous for this allele where intermediate in both plant size and 18:0 content between wild-type Arabidopsis and fab2-1 mutants. The alleles at fab2 and the suppressor mutations provided a total of nine genotypes which were analyzed to demonstrate a clear-cut relationship between leaf 18:0 content (0.7-19.6% of total leaf fatty acids) and reductions in plant size (24-4 mm). These results illustrate the utility of suppressor analysis for addressing problems in biochemistry and plant biology. They also indicate that the genetic control of plant lipid composition is more complex than previously appreciated.