Hiding in plain sight: the F segment and other conserved features of seed plant SK(n) dehydrins

An 11-residue amino acid sequence, DRGLFDFLGKK, is highly conserved in a subset of dehydrins found across the full spectrum of seed plants and here given the name F-segment. An 11-residue amino acid sequence, DRGLFDFLGKK, is highly conserved in identity and polarity in 130 non-redundant dehydrin sequences representing conifers and all major angiosperm groups. This newly described motif is here given the name F segment based on the pair of hydrophobic F residues at the core of the sequence. The majority of dehydrins previously classified as SK(n) dehydrins contain one F segment N terminal to the S and K segments and can accordingly be reclassified as FSK(n) dehydrins. A cysteine-containing variant, GCGMFDFLKK, occurs in a few rosid and asterid taxa. The S segment in this and other dehydrin types also includes previously overlooked conserved features, including a KLHR prefix and charged or G residues within and following the characteristic string of S residues. Secondary structure prediction models indicate that the F segment and S segment prefix may form amphipathic helices that could be involved in membrane or protein binding.