Seed storage proteins of Cupressaceae are homologous to legumins from angiosperms: Molecular characterization of cDNAs from incense cedar (Calocedrus decurrens [Torr] Florin)

Legumins are shown to be the predominant storage proteins present in the detergent soluble fractions of seeds from incense cedar and from all other Cupressaceae investigated. The subunits of these proteins are made up of alpha- and beta-polypeptides with molecular weights in the range of 30-34 kDa and 23-25 kDa, respectively. Unusual for legumins, those from incense cedar are glycosylated. An incense cedar endosperm cDNA library was constructed and three different legumin cDNAs were characterized; they represent two divergent legumin subfamilies with nucleotide similarities of about 71%. Comparisons with legumins from gymnosperms and angiosperms reveal between 57% and 34% identity on the amino acid level. The deduced amino acid sequences suggest that incense cedar legumins are synthesized as precursors to be processed similarly as is known from those of angiosperms. However, none of them contains the posttranslational cleavage site, Asn-Gly, which is assumed to be highly conserved in angiosperm legumin precursors. A phylogenetic analysis suggests that both legumin subfamilies described here originated relatively soon after divergence of the genes derived from the common ancestor of Pinaceae and Cupressaceae legumins. Moreover, legumins prove to be reliable molecular markers to elucidate seed plant relationships.