The polymerase chain reaction was used to survey gymnosperm legumin genes. Characterization of 46 cloned amplificates, differing in sequence and size (1.2-1.6 kb), revealed the ubiquitous occurrence of legumin genes and their organization in small subfamilies in the 22 species investigated. The 3' portions of the genes, coding for the legmnin fi-polypeptides, show a highly conserved intronlexon structure divergent from those of angiosperms: an additional intron (intron IV) uniformly interrupts the region coding for the C-terminal part of the P-polypeptides. Phylogenetic analysis of the respective coding sequences as well as the organization of the Magnolia B14 legumin gene also investigated here both indicate that intron IV is ancestral and was lost during early angiosperm evolution. Taking into account the intronlexon structures from all legumin genes known, our results suggest that legumln genes evolved by subsequent loss of introns, providing also further evidence for a common origin of legumins and vicilins.

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Analysis of legumin-encoding cDNAs from Dioscorea caucasica Lipsky (Dioscoreaceae) and from Asarum europaeum L. (Aristolochiaceae) shows that there is an especially methionine-rich legumin subfamily present in the lower angiosperm clades including the Monocotyledoneae. It is characterized by a methionine content of 3-4 mol% which is roughly triple the methionine proportion of most other legumins. These "MetR" legumins, if present, still have to be detected in the higher angiosperms including the important seed crops. Evolutionary analysis suggests that the MetR legumins are the result of a gene duplication allowing the differentiation of legumin genes according to their sulfur content. The duplication event must have taken place before the split into mono- and dicotyledonous plants but probably after the separation of angiosperms and gymnosperms.

Abstract. Analysis of legumin-encoding cDNAs fromDioscorea caucasica Lipsky (Dioscoreaceae) and from Asarum europaeum L. (Aristolochiaceae) shows that there is an especially methionine-rich legumin subfamily present in the lower angiosperm clades including the Monocotyledoneae. It is characterized by a methionine content of 3-4 mol% which is roughly triple the methionine proportion of most other legumins. These "MetR" legumins, if present, still have to be detected in the higher angiosperms including the important seed crops. Evolutionary analysis suggests that the MetR legumins are the result of a gene duplication allowing the differentiation of legumin genes according to their sulfur content. The duplication event must have taken place before the split into mono-and dicotyledonous plants but probably after the separation of angiosperms and gymnosperms.