Dehydrins, PpDHNA and PpDHNB from Physcomitrella patens provide drought and cold tolerance while PpDHNC shows antimicrobial property suggesting different dehydrins perform separate functions in P. patens. The moss Physcomitrella patens can withstand extremes of environmental condition including abiotic stress such as dehydration, salinity, low temperature and biotic stress such as pathogen attack. Osmotic stress is inflicted under both cold and drought stress conditions where dehydrins have been found to play a significant protective role. In this study, a comparative analysis was drawn for the three dehydrins PpDHNA, PpDHNB and PpDHNC from P. patens. Our data shows that PpDHNA and PpDHNB play a major role in cellular protection during osmotic stress. PpDHNB showed several fold upregulation of the gene when P. patens was subjected to cold and osmotic stress in combination. PpDHNA and PpDHNB provide protection to enzyme lactate dehydrogenase under osmotic as well as freezing conditions. PpDHNC possesses antibacterial activity and thus may have a role in biotic stress response. Overexpression of PpDHNA, PpDHNB and PpDHNC in transgenic tobacco showed a better performance for PpDHNB with respect to cold and osmotic stress. These results suggest that specific dehydrins contribute to tolerance of mosses under different stress conditions.

Plants can produce their own set of defense molecules in an attempt to survive under stressed conditions. Dehydrins play a considerable role in protecting the plants under varied stress situations. We have isolated a novel SK3 type dehydrin from Sorghum capable of protecting the enzyme lactate dehydrogenase in vitro under both cold and high temperature. This protein showed non-canonical migration in a sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) due to the high hydrophilicity of the protein. The high percentage of glycine and histidine residues present in the protein sequence is responsible for the radical scavenging activity of the protein. The protein also exhibited binding affinity to metal ions owing to the histidine-rich motifs, therefore chelating the metal ions and making them unavailable to systems responsible for generation of reactive oxygen species (ROS). In the presence of specific metal ions, the protein showed reversible aggregation with certain degree of protease resistivity along with induction of secondary structures. The resistivity of the protein to degradation might be implicated in stress situations, thus leading to an increase in the shelf life of the protein. Association with metal ions like copper and zinc at a fairly low concentration increased the protective effect of the SbDHN2 protein for lactate dehydrogenase (LDH) activity to a considerable extent. The synthesis of this dehydrin in stressed plants might help the plant in rendering stress tolerance.

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The promoter deletion mutants from second isoform of INO1 (gene-encoding MIPS) from Porteresia coarctata of 932 bp (pPcINO1.2.932) and 793 bp (pPcINO1.2.793) prove to be very efficient as salt/drought stress-inducible promoters, while pPcINO1.2.932 is found to be responsive to cold stress as well. The promoters of the two identified myo-inositol-1-phosphate synthase (INO1) isoforms from salt-tolerant wild rice, Porteresia coarctata (PcINO1.1 and PcINO1.2) have been compared bioinformatically with their counterparts present in the salt-sensitive rice, Oryza sativa. PcINO1.2 promoter was found to be enriched with many abiotic stress-responsive elements, like abscisic acid-responsive elements, MYC-responsive elements, MYB-binding sites, low-temperature stress-responsive elements, and heat-shock elements similar to the ones found in the conserved motifs of the promoters of salt/drought stress-inducible INO1 promoters across Kingdom Planta. To have detailed analysis on the arrangement of cis-acting regulatory elements present in PcINO1 promoters, 5' deletion mutational studies were performed in dicot model plants. Both transient as well as stable transformation methods were used to check the influence of PcINO1 promoter deletion mutants under salt and physiologically drought conditions using β-glucuronidase as the reporter gene. The deletion mutant from the promoter of PcINO1.2 of length 932 bp (pPcINO1.2.932) was found to be significantly upregulated under drought stress and also in cold stress, while another deletion mutant, pPcINO1.2.793 (of 793 bp), was significantly upregulated under salt stress. P. coarctata being a halophytic species, the high inducibility of pPcINO1.2.932 upon exposure to low-temperature stress was an unexpected result.

Plants use a diverse set of proteins to mitigate various abiotic stresses. The intrinsically disordered protein dehydrin is an important member of this repertoire of proteins, characterized by a canonical amphipathic K-segment. It can also contain other stress-mitigating noncanonical segments—a likely reflection of the extremely diverse nature of abiotic stress encountered by plants. Among plants, the poikilohydric mosses have no inbuilt mechanism to prevent desiccation and therefore are likely to contain unique noncanonical stress-responsive motifs in their dehydrins. Here we report the recurring occurrence of a novel amphipathic helix-forming segment (D-segment: EGφφD(R/K)AKDAφ, where φ represents a hydrophobic residue) in Physcomitrella patens dehydrin (PpDHNA), a poikilohydric moss. NMR and CD spectroscopic experiments demonstrated the helix-forming tendency of the D-segment, with the shuffled D-segment as control. PpDHNA activity was shown to be size as well as D-segment dependent from in vitro , in vivo , and in planta studies using PpDHNA and various deletion mutants. Bimolecular fluorescence complementation studies showed that D-segment-mediated PpDHNA self-association is a requirement for stress abatement. The D-segment was also found to occur in two rehydrin proteins from Syntrichia ruralis , another poikilohydric plant like P. patens . Multiple occurrences of the D-segment in poikilohydric plant dehydrins/rehydrins, along with the experimental demonstration of the role of D-segment in stress abatement, implies that the D-segment mediates unique resurrection strategies, which may be employed by plant dehydrins that are capable of mitigating extreme stress.