XvVHA-c''1- a novel stress-responsive V-ATPase subunit c'' homologue isolated from the resurrection plant Xerophyta viscosa

The strategy of 'complementation by functional sufficiency' was used to isolate XvVHA-c''1, a vacuolar adenosine triphosphatase (V-ATPase) proteolipid subunit c'' homologue from Xerophyta viscosa. XvVHA-c''1 rescued Escherichia coli srl::Tn10 mutants that were subjected to a 1.2 M sorbitol osmotic stress. Bioinformatics analyses conducted on XvVHA-c''1 revealed all signature characteristics that are common amongst subunit c homologues, which include the four transmembrane domain motifs and a conserved glutamate residue in the fourth transmembrane domain. XvVHA-c''1 shares 90.96% identity with the Oryza sativa (japonica) subunit c homologue and 86.67% identity with a putative vacuolar ATP synthase proteolipid subunit c' from Arabidopsis thaliana, at the amino acid level. Southern hybridization analysis conducted on X. viscosa genomic DNA confirmed the presence of XvVHA-c''1 in the X. viscosa genome. Northern hybridization analysis was conducted on X. viscosa tissue subjected to NaCl stress, dehydration and - 20 degree C shock, in response to which upregulated transcript levels of XvVHA-c''1 were seen. XvVHA-c''1's functional relevance was established through complementation using a Saccharomyces cerevisiae vma3 knockout.