AN ALLELE OF A GENE ENCODING A Y₂K DEHYDRIN THAT IS HIGHLY EXPRESSED IN SEED CO-SEGREGATES WITH CHILLING TOLERANCE DURING SEEDLING EMERGENCE IN COWPEA

Department of Botany and Plant Sciences, University of California, Riverside, CA, USA

Dehydrins (DHNs; LEA D-11) are lipid-associating proteins involved in the adaptive response of plants to drought, low temperature and salinity. DHNs are encoded by multigene families in higher plants. We discovered in cowpea (Vigna unguiculata) that a 26.5 kDa Y₂K-type dehydrin, DHN1, is very abundant in the seeds of some genotypes but not detectable in others. From our initial studies of genetically closely related cowpea breeding lines, we developed a model for the dependence of chilling tolerance during seedling emergence on two additive and independent factors: 1) the presence (versus absence) of DHN1 in the seed, and 2) the extent of electrolyte leakage from seeds at chilling temperature. In subsequent genetic linkage tests, we found that allelic differences in the cowpea Dhn1 structural gene map to the same position on a cowpea genetic linkage map as the DHN1 protein presence/absence trait. Also, after backcrosses that produced near-isogenic lines, the presence of the DHN1 protein in seed and the corresponding Dhn1 allele remained genetically associated with chilling tolerance during seedling emergence, independent of electrolyte leakage effects. Allelic variation in the Dhn1 gene, therefore, seems to be one component of heritable variation in low temperature seedling emergence in cowpea. Because of the independence of the effect of the Dhn1 gene and electrolyte leakage, the function of the DHN1 protein would seem to be unrelated to protection of the plasma membrane, which is the primary lesion point related to electrolyte leakage.