GENETIC-VARIATION IN PEA (PISUM) DEHYDRINS - SEQUENCE ELEMENTS RESPONSIBLE FOR LENGTH DIFFERENCES BETWEEN DEHYDRIN ALLELES AND BETWEEN DEHYDRIN LOCI IN PISUM-SATIVUM L

The electrophoretic patterns of dehydrins extracted from mature seeds of a range of pea (Pisum) species revealed extensive variation in dehy drin polypeptide mobility. Variation was also observed among lines of P. sativum. Crosses between lines with different dehydrin electrophore tic patterns produced F-1 seeds with additive patterns, and segregatio n in the F-2 generation was consistent with a 1:2:1 ratio, indicating allelic variation at each of two dehydrin loci (Dhn2, Dhn3). Genetic l inkage was observed between Dhn2 and Dhn3, and the segregation ratios indicated preferential transmission of one allele at the Dhn3 locus. D ehydrin cDNA clones were characterised that encoded the allelic varian ts at Dhn2 and Dhn3. Their deduced amino-acid sequences were very simi lar to each other as well as to the product of the Dhn1 locus reported previously. Comparisons were made between the sequences of allelic va riants at a single locus, and between the products of different loci. Differences in the electrophoretic mobilities between allelic variants at Dhn2 and Dhn3 were associated with differences in polypeptide leng th resulting principally from tandem duplications of 21 (Dhn2) or 24 ( Dhn3) amino-acid residues. These duplications accounted for much of th e difference in length between dehydrins encoded by the different loci . The conserved core of one of the duplicated regions varied in copy n umber, and small insertions/deletions of amino acids near this core al so contributed to length variation both between allelic forms and betw een loci. Dehydrins possess characteristic highly conserved amino-acid sequence motifs, yet vary considerably in length. Mechanisms involvin g sequence duplication appear to be responsible for generating the len gth differences observed between allelic variants as well as between t he products of different loci.