CHARACTERIZATION OF A NEW CLASS OF OLEOSINS SUGGESTS A MALE GAMETOPHYTE-SPECIFIC LIPID STORAGE PATHWAY

The expression and sequences of two related anther-specific cDNAs (13 and C98) of Brassica napus (oilseed rape) were examined. These cDNAs w ere found to exhibit significant predicted amino acid sequence similar ity with a group of seed-specific proteins, the oleosins, which are in volved in oil body membrane structure. Pollen of B. napus also contain s oil bodies, and the synthesis and accumulation of these organelles c orrelates with expression of the 13 and C98 transcripts. The protein c ontent of purified pollen oil bodies was therefore examined in order t o determine the presence or absence of possible oleosins. One major pr otein species of 14 kDa was identified and subjected to N-terminal ami no acid sequence determination. The sequence of this pollen oil body a ssociated protein is homologous to the predicted sequence of one of th e anther-specific cDNAs, 13, implying that this cDNA represents an ant her-specific oleosin gene expressed in developing pollen. The expressi on of other genes active during seed oil body formation was also exami ned, and these were found to be specific to the sporophyte, inferring the existence of specific components of the pathway of lipid synthesis and storage in the male gametophyte. These possibilities and the rela tionship between different oleosin genes are discussed.