Identification of differentially expressed proteins of Arthrospira (Spirulina) plantensis-YZ under salt-stress conditions by proteomics and qRT-PCR analysis.

Arthrospira (Spirulina) platensis as a representative species of cyanobacteria has been recognized and used worldwide as a source of protein in the food, which possesses some unusual and valuable physiological characteristics, such as alkali and salt tolerance. Based on complete genome sequencing of Arthrospira (Spirulina) plantensis-YZ, we compared the protein expression profiles of this organism under different salt-stress conditions (i.e. 0.02 M, 0.5 M and 1.0 M NaCl, respectively), using 2-D electrophoresis and peptide mass fingerprinting, and retrieved 141 proteins showing significantly differential expression in response to salt-stress. Of the 141 proteins, 114 Arthrospira (Spirulina) plantensis-YZ proteins were found with significant homology to those found in Arthrospira (76 proteins in Arthrospira platensis str. Paraca and 38 in Arthrospira maxima CS-328). The remaining 27 proteins belong to other bacteria. Subsequently, we determined the transcriptional level of 29 genes in vivo in response to NaCl treatments and verified them by qRT-PCR. We found that 12 genes keep consistency at both transcription and protein levels, and transcription of all of them but one were up-regulated. We classified the 141 differentially expressed proteins into 18 types of function categories using COG database, and linked them to their respective KEGG metabolism pathways. These proteins are involved in 31 metabolism pathways, such as photosynthesis, glucose metabolism, cysteine and methionine metabolism, lysine synthesis, fatty acid metabolism, glutathione metabolism. Additionally, the SRPs, heat shock protein and ABC transporter proteins were identified, which probably render Arthrospira (Spirulina) plantensis's resistance against high salt stress.