Allelic variation of a dehydrin gene cosegregates with chilling tolerance during seedling emergence

Dehydrins (DHNs, LEA D-ll) are plant proteins present during environmental stresses associated with dehydration or low temperatures and during seed ma turation, Functions of DHNs have not yet been defined. Earlier, we hypothes ized that a approximate to 35-kDa DHN and membrane properties that reduce e lectrolyte leakage from seeds confer chilling tolerance during seedling eme rgence of cowpea (Vigna unguiculata L. Walp,) in an additive and independen t manner. Evidence for this hypothesis was not rigorous because it was base d on correlations of presence/absence of the DHN and slow electrolyte leaka ge with chilling tolerance in closely related cowpea lines that have some o ther genetic differences. Here, we provide more compelling genetic evidence for involvement of the DHN in chilling tolerance of cowpea. We developed n ear-isogenic lines by backcrossing, We isolated and determined the sequence of a cDNA corresponding to the approximate to 35-kDa DHN and used gene-spe cific oligonucleotides derived from it to test the genetic linkage between the DHN presence/absence trait and the DHN structural gene. We tested for a ssociation between the DHN presence/absence trait and both low-temperature seed emergence and electrolyte leakage. We show that allelic differences in the Dhn structural gene map to the same position as the DHN protein presen ce/absence trait and that the presence of the approximate to 35-kDa DHN is indeed associated with chilling tolerance during seedling emergence, indepe ndent of electrolyte leakage effects. Two types of allelic variation in the Dhn gene were identified in the protein-coding region, deletion of one Phi -segment from the DHN-negative lines and two single amino acid substitution s.