ABSTRACT
Lipid transfer proteins (LTPs) are small, basic and abundant proteins in higher plants. They are capable of binding fatty acids and of transferring phospholipids between membranes in vitro. LTPs from this family contain a signal peptide and are secreted in the cell wall. Their biological function is presently unknown. LTPs have been suggested to participate to cutin assembly and to the defense of the plants against pathogens. A genetic approach should prove useful to provide clues on their in vivo functions. Here, the characterization of the LTP gene family in Arabidopsis thaliana is described. At least 15 genes were identified, their map position determined and the expression pattern characterized for six of them. All the sequences exhibit the typical features of plant LTPs. The molecular weight is close to 9 kDa, the isoelectric point is near 9 (except for three acidic LTPs), and typical amino acid residues such as cysteines are conserved. Genomic DNA blotting hybridization experiments performed using ltp1 to ltp6 as probes indicate that ltps form distinct 1-3 gene subfamilies which do not cross hybridize. Expression studies indicate that all the genes tested are expressed in flowers and siliques, but not in roots. Ltp1, ltp5 and ltp2 are expressed significantly in leaves, while ltp6 is detected only in 2-4-week-old leaves. In addition, ltp4 and ltp3 are strongly upregulated by abscisic acid (ABA). Tandem repeats can be noted concerning ltp1 and ltp2 on chromosome 2, ltp3 and ltp4 on chromosome 5 and ltp5 and ltp12 on chromosome 3. While ltp7, ltp8 and ltp9 map at the same position on chromosome 2, the other genes are dispersed throughout the genome. The characterization of the Arabidopsis ltp gene family will permit to initiate a genetic approach for determining the in vivo function(s) of these proteins.
