Dehydrin variability among rhododendron species: a 25-kDa dehydrin is conserved and associated with cold acclimation across diverse species.

•  Here we examine the accumulation pattern of dehydrins in non- vs cold-acclimated leaves of 21 species comprising two divergent groups of Rhododendron, Subgenus Hymenanthes and Subgenus Rhododendron. Individuals from five other Ericaceous genera were also evaluated in the same way. Quantitative comparisons of cold-inducibility of a 25-kDa dehydrin and cold acclimation ability in six Rhododendron species were also performed. •  Leaf freezing tolerance assay and dehydrin detection and quantification were performed as previously described. •  Eleven dehydrins, ranging from 25- to 73-kDa, were observed among the 21 species, and most were more abundant in winter-collected leaves than in summer-collected leaves. One dehydrin, a 25-kDa protein, was uniquely conserved across most (95%) of the species surveyed, and was absent only in R. brookeanum, a tropical species that may not be capable of cold acclimation. The 25-kDa dehydrin was also identified in Kalmia, a genus closely related to Rhododendron but not in four other less related Ericaceous genera. Comparison of dehydrin profiles in non- and cold-acclimated leaf tissue from six species (three very hardy, and three less hardy, species) indicated a close association (R2  = 0.95) between relative changes in leaf freezing tolerance and 25-kDa dehydrin accumulation. •  The taxonomic and physiological comparisons suggest a central, but as yet unknown, function for the 25-kDa dehydrin in protecting rhododendron leaves from freezing injury.