The Evolution And Secretion Of WSPA Protein And Its Potential Role In Stress Resistance In N.flagelliforme

Nostoc flagelliforme is a filamentous cyanobacterium usually called "Facai" in China.It distributes in the north and west-north of China and shows marked resistance to desiccation,UV-B and salt stresses.N.flagelliforme serves as a potential model material for investigating abiotic sress resistance mechanisms in cyanobacteria.WSPA is an abundant acid soluble protein that was first found in Nostoc commune.It accounts for more than 70%of the total soluble protein in it and can be partially secreted into extracellular polysaccharide(EPS)matrix upon rehydration.This protein can be induced by desiccation stress and UV-B treatment.Previous study in our group has found that WSPA also exists in two other species,N.flagelliforme and N.sphaeroides.Blast analyis did not find any similar protein from other sequenced cyanobacteria in public databases.Thus,we inferred that WSPA is a unique protein in macroscopic Nostoc species.Does WSPA contain any conservative domains?How WSPA is partially transported into EPS sheath?Whether WSPA plays a role in stress resistance?These questions are needed to be explored.Western blot and commassie blue staining showed that the molecular size and abundance of WSPA homologs differed in a certain extent in N.flagelliforme and N.commune samples collected from different locations.This difference may imply different environmental stress pressures exerted on these samples.WSPA is abundant in natural colonies of N.flagelliforme,but can not be detected in long-term liquid-cultured colonies of N.flagelliforme.UV-B,NaCl,mannitol and desication treatments could induce the wpsa transcription in the former,but could not in the latter.Liquid-cultured N.flagelliforme is not very resistant to desiccation stress.Therefore,these results implied that wspa is tightly related to stress response in natural N.flagelliforme.Bioinformatic analysis of various WSPAs found that partial N-terminal sequence of WSPA is quite conservative.Through fractional expression of wspa,fused with gfp reporter gene in Nostoc sp.PCC 7120,we found that the N-terminal sequence is associated with the secreation of WSPA into EPS sheath In addition,wspa-expressing Nostoc Sp.PCC 7120 exhibited resistance to various abiotic stresses.Finally,we screened the cDNA library to find those proteins potentially interacted with WSPA.In general,we conducted the researches on the evolution,secretion and function of WSPA,These are of great significance to understand the molecular mechanism of N.flagelliforme adapting to environmental stresses.