Isolation of a cDNA from Arabidopsis thaliana that complements the sec14 mutant of yeast

The SEC14 gene of Saccharomyces cerevisiae codes for a phosphatidylinositol-transfer protein (Sec14p(sc)) which is capable of transferring both phosphatidylinositol and phosphatidylcholine between membranes in vitro. Genetic and biochemical studies conducted in S. cerevisiae have shown that this protein acts as an inhibitor of phosphatidylcholine biosynthesis via the so-called Kennedy pathway only. This inhibition is controlled by the binding of phospholipids to the Sec14p(sc) protein. Here we describe the isolation of a cDNA from Arabidopsis thaliana by functional complementation of a sec14(ts) mutant of S. cerevisiae. This cDNA, designated AtSEC14, is capable of restoring the growth of the sec14(ts) mutant at the restrictive temperature of 37 degrees C. Extracellular invertase measurements indicated that the cDNA can partly restore protein secretion. In addition, the phosphatidylinositol-transfer activity measured in protein extracts is greatly enhanced in the complemented mutant strain when compared with the sec14(ts) mutant. The best sequence similarity at the amino acid level is found with the Sec14p protein of S. cerevisiae (36.5% similarity), and most of the amino acids that an thought to be involved in the binding of phospholipids in the yeast protein are conserved in the AtSEC14 gene product. Southern analysis suggests the presence of a single gene in the Arabidopsis genome, although the existence of distantly related sequences cannot be excluded. This gene is expressed in roots, leaves, flowers and siliques of Arabidopsis.