SEQUENCE PECULIARITY OF GNETALEAN LEGUMIN-LIKE SEED STORAGE PROTEINS

The development of seeds as a specialized organ for the nutrition, pro tection, and dispersal of the next generation was an important step in the evolution of land plants, Seed maturation is accompanied by massi ve synthesis of storage compounds such as proteins, starch, and Lipids . To study the processes of seed storage protein evolution we have par tially sequenced storage proteins from maturing seeds of representativ es from the gymnosperm genera Gnetum, Ephedra, and Welwitschia-morphol ogically diverse and unusual taxa that are grouped In most formal syst ems into the common order Gnetales. Based on partial N-tenminal amino acid sequences, oligonucleotide primers were derived and used for PCR amplification and cloning of the corresponding cDNAs, We also describe the structure of the nuclear gene for legumin of Welwitschia mirabili s. This first gnetalean nuclear gene structure contains introns in onl y two of the four conserved positions previously characterized in othe r spermatophyte legumin genes; The distinct phylogenetic status of the gnetalean taxa is also reflected in a sequence peculiarity of their l egumin genes. A comparative analysis of exon/intron sequences leads to the hypothesis that legumin genes from Gnetales belong to a monophyle tic evolutionary branch clearly distinct from that of legumin genes of extant Ginkgoales and Coniferales as well as from all angiosperms.