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 phosph atidylinositol and phosphatidylcholine between membranes in vitro. Genetic and biochemical studies conducted in S. cerevisiae have shown that this pro tein acts as an inhibitor of phosphatidylcholine biosynthesis via the so-ca lled 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(t s) mutant of S. cerevisiae. This cDNA, designated AtSEC14, is capable of re storing the growth of the sec14(ts) mutant at the restrictive temperature o f 37 degrees C. Extracellular invertase measurements indicated that the cDN A can partly restore protein secretion. In addition, the phosphatidylinosit ol-transfer activity measured in protein extracts is greatly enhanced in th e complemented mutant strain when compared with the sec14(ts) mutant. The b est sequence similarity at the amino acid level is found with the Sec14p pr otein 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 pro tein are conserved in the AtSEC14 gene product. Southern analysis suggests the presence of a single gene in the Arabidopsis genome, although the exist ence of distantly related sequences cannot be excluded. This gene is expres sed in roots, leaves, flowers and siliques of Arabidopsis.