EVOLUTION OF THE GROUP-1 LATE EMBRYOGENESIS ABUNDANT (LEA) GENES - ANALYSIS OF THE LEA B19 GENE FAMILY IN BARLEY

The highly conserved Group 1 late embryogenesis abundant (Lea) genes a re present in the genome of most plants as a gene family. Family membe rs are conserved along the entire coding region, especially within the extremely hydrophilic internal 20 amino acid motif, which may be repe ated. Cloning of Lea Group 1 genes from barley resulted in the charact erization of four family members named B19.1, B19.1b, B19.3 and B19.4 after the presence of this motif 1, 1, 3 and 4 times in each gene, res pectively. We present here the results of comparative and evolutionary analyses of the barley Group 1 Lea gene family (B19). The most import ant findings resulting from this work are (1) the tandem clustering of B19.3 and B19.4, (2) the spatial conservation of putative regulatory elements between the four B19 gene promoters, (3) the determination of the relative 'age' of the gene family members and (4) the 'chimeric' nature of B19.3 and B19.4, reflecting a cross-over or gene-conversion event in their common ancestor. We also show evidence for the presence of one or two additional expressed B19 genes in the barley genome. Ba sed on our results, we present a model for the evolution of the family in barley, including the 20 amino acid motif. Comparisons of the rela tedness between the barley family and all other known Group 1 Lea gene s using maximum parsimony (PAUP) analysis provide evidence for the tim e of divergence between the barley genes containing the internal motif as a single copy and as a repeat. The PAUP analyses also provide evid ence for independent duplications of Group 1 genes containing the inte rnal motif as a repeat in both monocots and dicots.