Function of lipid transfer protein and its homologus proteins in plant cells

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1. Function of lipid transfer protein (LTP) and its homologus proteinsLPT was isolated as a protein which transfers polar lipids between biomembranes in vitro, but it is unlikely that LTP functions in vivo for intracellular lipid trasfer. LTPs did not occur in cytosol but in density vesicles in cells and cell walls. The expression of LTP genes and the accumulation of LTPs were observed in the surface area of developing organs such as embryos, endosperms and primordia of leaves and floweres. In addition, LTPs have the capacities of binding fatty acids and acylCoAs. From these results. LTP seems to functions in vivo as a carrier of wax or cutin monomers. This assumption was supported by evidence that wax synthesis induced by UV irradiation in cucmber leaves was followed by the accumulation of LTPs in the cuticles. On the other hand , the localization of LTPs in density vesicles in castor bean cotyledon cells and assembly of these vesicles into a vacuoles remains unsolved.2. Cloning of LTP genes and its homologus protein genesThere are organ-specific isoforms of LTP, A - D, in castor bean seedlings. We cloned the isoform C gene by PCR method using the isoform C _cDNA.Intron sturucture of the isoform C gene has been determined, but its promoter structure has not, because of unsuccessfulness in isolating the upstream region of LTP gene. Several clones have been isolated from genomic library prepared from castor bean cotyledons and the analysis of nucleotides is in progress.Eight cysteines in LTP sequence were conservative. To examine the role of these cysteines for binding of LTP to fatty acid, the isoform C _cDNA was modified to yield the isoform C with serines instead the cysteines and the modified LTP is now to be expressed.