Organ-specific occurrence and expression of the isoforms of nonspecific lipid transfer protein in castor bean seedlings, and molecular cloning of a full-length cDNA for a cotyledon-specific isoform.

Four kinds of nonspecific lipid transfer proteins (nsLTP) were purified from different organs of castor bean (Ricinus communis L.) seedlings. Amino acid compositions and amino-terminal sequences of the four nsLTPs were determined and compared with those of castor bean isoforms, nsLTP-A, -B, and -C, previously reported [Takishima et al. (1986) Biochim. Biophys. Acta 870, 248-255; Takishima et al. (1988) Eur. J. Biochem. 177, 241-249]. Two isoforms from the cotyledons were identified as nsLTP-A and -C, one isoform from the endosperms as nsLTP-B, and the other was a new isoform from the axes. This new isoform was named nsLTP-D and its amino acid sequence was determined. These results demonstrated organ-specific occurrence of the nsLTP isoforms in castor bean seedlings. The isoforms nsLTP-A, -B, -C, and -D showed similar transfer activity not only for phosphatidylcholine and phosphatidylethanolamine but also for monogalactosyldiacylglycerol, although the homology among their amino acid sequences ranged from 70 to 30%. Two cDNA clones (pnsLTP-C and pnsLTP-D) for nsLTPs of castor bean seedlings were isolated and sequenced. pnsLTP-C was the cDNA clone for nsLTP-C expressed in the cotyledons, and pnsLTP-D was that for nsLTP-D in the axis. A coupled in vitro transcription-translation analysis of both cDNA clones revealed that pnsLTP-C encodes the full-length of nsLTP-C precursor (pro-nsLTP-C), while pnsLTP-D encodes a part of nsLTP-D precursor. PronsLTP-C contained a 24-amino acid pre-sequence preceding the mature nsLTP-C (92 amino acids).(ABSTRACT TRUNCATED AT 250 WORDS)