Evolution of the modular, disordered stress proteins known as dehydrins

Dehydrins, plant proteins that are upregulated during dehydration stress conditions, have modular sequences that can contain three conserved motifs (the Y-, S-, and K-segments). The presence and order of these motifs are used to classify dehydrins into one of five architectures: K(n), SK(n), K(n)S, Y(n)K(n), and Y(n)SK(n), where the subscript n describes the number of copies of that motif. In this study, an architectural and phylogenetic analysis was performed on 426 dehydrin sequences that were identified in 53 angiosperm and 3 gymnosperm genomes. It was found that angiosperms contained all five architectures, while gymnosperms only contained K(n) and SK(n) dehydrins. This suggests that the ancestral dehydrin in spermatophytes was either K(n) or SK(n), and the Y-segment containing dehydrins first arose in angiosperms. A high-level split between the Y(n)SK(n) dehydrins from either the K(n) or SK(n) dehydrins could not be confidently identified, however, two lower level architectural divisions appear to have occurred after different duplication events. The first likely occurred after a whole genome duplication, resulting in the duplication of a Y(3)SK(2) dehydrin; the duplicate subsequently lost an S- and K- segment to become a Y(3)K(1) dehydrin. The second split occurred after a tandem duplication of a Y(1)SK(2) dehydrin, where the duplicate lost both the Y- and S- segment and gained four K-segments, resulting in a K(6) dehydrin. We suggest that the newly arisen Y(3)K(1) dehydrin is possibly on its way to pseudogenization, while the newly arisen K(6) dehydrin developed a novel function in cold protection.