# Order in Chaos: Lesser-Conserved and Repeat Structures in Dehydrins
## 4 Discussion
### Delhydrins in Early Land Plant Evolution  
Herein is, as far as I know, the first report of confirmed Dhn sequences in green algae. None of the green algal sequences identified by Dehydrin Decoder included H, F, or Y segments, all of which appear to have evolved later in land plant evolution. One SK1 Dhn and one SK2 Dhn were found in _Klebsormidium nitens_, a filamentous alga that occurs in terrestrial environments, including desert soil crusts subject to severe desiccation, suggesting that the S segment may have evolved during adaptation to terrestrial or periodically dry environments. The pseudo K1 and K2 Dhns in _Symbiochloris_ and the additional K12 Dhn in _Myrmecia_ are of interest because these genera represent the main family of lichen photosymbionts, the Trebouxiaceae, wherein tolerance of rapid cycles of desiccation and rehydration are part of the lifestyle. [PERSON] et al. (2018) provided immunological evidence of Dhns in the lichen symbiont _Trebouxia erici_, but this seems to be the first report of a confirmed Dhn sequences for lichen photobionts. The K segments in the Kn algal Dhns (i.e., the C-terminal K segment in the _Klebsormidium_ SK2 Dhn GAQ85800.1, EKKGFFKKIEEKLTG, score 8.35), generally conserve the identity or properties of the residues in the canonical K segment land plant Dhns. BLASTp searches on the full sequences of the algal Kn Dhns did not return any strong alignments with bryophyte or other land plant Dhns, perhaps not surprising given the evolutionary distance between these groups and the unstructured and highly variable character of Dhns. The majority of the green algal sequences were classified as pseudo Dhns with single, low scoring variants of the K segment. Allowing for modification of the K segment in land plant evolution, some or all of these may be functional Dhns with ancestral characteristics. Dhn-like proteins have been detected immunologically in brown rockweeds (Kal  
description of the H segment. The authors also documented consistent differences in the pI, Gravy index, and fold index among the three Dhn orders. Their findings are supported by my LDA analysis of amino acid composition (Figure 3), which clearly delineates the three main groups, leaving about 600 Kn and SKn Dhns unclassified. A total of 15 of the 307 sequences in [PERSON] et al. 's analysis lacked H, F, or Y segments, but 1, 2, and 12 of these were placed in the above-named orders, respectively, many with > 90% bootstrap support, indicating a possible origin by deletion of an accessory segment. However, the known Dhns in algal groups lack any of these accessory segments and bryophytes lack H and F segments, suggesting that some Kn and SKn Dhns may represent basal Dhn types that evolved before the origin of additional segments. Despite wide variability in sequence and length within and between taxa, each order can be characterized by a typical or consensus structure composed of a predictable order of conserved segments separated by somewhat more variable transitional regions with some conservation in amino acid composition and structure, and phi segments that are highly variable in length and composition. Reading from the N to C terminus, a typical (H)KnS Dhn has the following segments:  
* A single H segment at the N terminus. * A random coil phi segment. * Usually one K segment with the variant consensus HKEGFVDKIKDKIHG, separated by highly variable phi segments. * A variable length transitional segment comprised of Gly and charged residues interrupted by a poly-K region and with His residues at the C-terminal or both ends. * A single C-terminal S segment. (H)KnS Dhns almost always have conserved segments at both ends, unlike the other orders, which typically have N-terminal prefixes and C-terminal suffixes that vary widely in length and composition.