Identification and characterization of Rab7 from orange-spotted grouper, Epinephelus coioides

• A novel Rab7 gene was identified from grouper Epinephelus coioides.
• Ec-Rab7 partly colocalized with lysosome, and incorporated into virus assembly sites at the late stage of infection.
• Overexpression of Ec-Rab7 in vitro accelerated SGIV infection.
• Ec-Rab7 might interact with viral protein SGIV ORF69 and ORF101.

Rab7 is a small GTPase that regulates vesicular traffic from early to late endosomal stages of the endocytic pathway. During the virus–host co-evolution, host Rab7 was also exploited by virus to complete their life cycle. To date, however, the roles of fish Rab7 in virus infection remained largely unknown. Here, we cloned and characterized a Rab7 gene from grouper, Epinephelus coioides (Ec-Rab7). The full-length Ec-Rab7 cDNA was composed of 1182 bp and encoded a polypeptide of 207 amino acids which shared 99% identity with that from Anoplopoma fimbria or Oreochromis niloticus. Ec-Rab7 contained five conserved domains of Rab GTPase family including GTP-binding or GTPase regions as well as an effector site. RT-PCR analysis revealed that Ec-Rab7 ubiquitously expressed in all detected tissues and its transcript in spleen was up-regulated after challenge with Singapore grouper iridovirus (SGIV). Subcellular localization analysis revealed that Ec-Rab7 was distributed in the cytoplasm as spots and mostly colocalized with lysosomes. Notably, the ectopic expressed Ec-Rab7 partly aggregated into the viral factories in cells infected by SGIV. Furthermore, overexpression of Ec-Rab7 accelerated the occurrence of cytopathic effect (CPE) induced by SGIV infection and promoted viral gene transcription. In addition, far western blotting assay revealed that Ec-Rab7 might interact with viral proteins, including SGIV VP69 and VP101. Taken together, our data suggested that Ec-Rab7 might be potentially involved in SGIV replication.