AUTHOR=Wei Hui , Yang Yongfu , Himmel Michael E. , Tucker Melvin P. , Ding Shi-You , Yang Shihui , Arora Rajeev 

TITLE=Identification and Characterization of Five Cold Stress-Related Rhododendron Dehydrin Genes: Spotlight on a FSK-Type Dehydrin With Multiple F-Segments

JOURNAL=Frontiers in Bioengineering and Biotechnology

VOLUME=7

YEAR=2019

URL=https://www.frontiersin.org/journals/bioengineering-and-biotechnology/articles/10.3389/fbioe.2019.00030

DOI=10.3389/fbioe.2019.00030

ISSN=2296-4185

ABSTRACT=<p>Dehydrins are a family of plant proteins that accumulate in response to dehydration stresses, such as low temperature, drought, high salinity, or during seed maturation. We have previously constructed cDNA libraries from <italic>Rhododendron catawbiense</italic> leaves of naturally non-acclimated (NA; leaf LT<sub>50</sub>, temperature that results in 50% injury of maximum, approximately −7°C) and cold-acclimated (CA; leaf LT<sub>50</sub> approximately −50°C) plants and analyzed expressed sequence tags (ESTs). Five ESTs were identified as dehydrin genes. Their full-length cDNA sequences were obtained and designated as <italic>RcDhn 1-5</italic>. To explore their functionality vis-à-vis winter hardiness, their seasonal expression kinetics was studied at two levels. Firstly, in leaves of <italic>R. catawbiense</italic> collected from the NA, CA, and de-acclimated (DA) plants corresponding to summer, winter and spring, respectively. Secondly, in leaves collected monthly from August through February, which progressively increased freezing tolerance from summer through mid-winter. The expression pattern data indicated that <italic>RcDhn 1-5</italic> had 6- to 15-fold up-regulation during the cold acclimation process, followed by substantial down-regulation during deacclimation (even back to NA levels for some). Interestingly, our data shows RcDhn 5 contains a histidine-rich motif near N-terminus, a characteristic of metal-binding dehydrins. Equally important, RcDhn 2 contains a consensus 18 amino acid sequence (i.e., ETKDRGLFDFLGKKEEEE) near the N-terminus, with two additional copies upstream, and it is the most acidic (pI of 4.8) among the five RcDhns found. The core of this consensus 18 amino acid sequence is a 11-residue amino acid sequence (DRGLFDFLGKK), recently designated in the literature as the F-segment (based on the pair of hydrophobic F residues it contains). Furthermore, the 208 orthologs of F-segment-containing RcDhn 2 were identified across a broad range of species in GenBank database. This study expands our knowledge about the types of F-segment from the literature-reported single F-segment dehydrins (FSK<sub>n</sub>) to two or three F-segment dehydrins: <italic>Camelina sativa</italic> dehydrin ERD14 as F<sub>2</sub>S<sub>2</sub>K<sub>n</sub> type; and RcDhn 2 as F<sub>3</sub>SK<sub>n</sub> type identified here. Our results also indicate some consensus amino acid sequences flanking the core F-segment in dehydrins. Implications for these cold-responsive RcDhn genes in future genetic engineering efforts to improve plant cold hardiness are discussed.</p>