The LEA family is composed of a diverse collection of multi-domain and multi-functional proteins, found in all three Domains of the Tree of Life, but particularly common in plants. Most members of the family are known to play an important role in abiotic stress response and stress tolerance in plants, but are also part of the plant hypersensitive response to pathogen infection. The mechanistic basis for LEA protein functionality is still poorly understood. The group of LEA 2 proteins harbour one or more copies of a unique domain, the [underln]W[/underln]ater stress and [underln]Hy[/underln]persensitive response (WHy) domain. This domain sequence has recently been identified as a unique ORF in some bacterial genomes (mostly in the phylum Firmicutes), and the recombinant bacterial WHy protein has been shown to exhibit a stress tolerance phenotype in E. coli and an in vitro protein denaturation protective function. Multi-domain phylogenetic analyses suggest that the WHy protein gene sequence may have ancestral origins in the Domain Archaea, with subsequent acquisition in Bacteria and Eukaryotes via endosymbiont or Horizontal Gene Transfer mechanisms.