Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in the downregulation of Bamboo mosaic virus and its associated satellite RNA Replication :: Biology, RNA

The association of host proteins with viral replicase complexes has been demonstrated in a number of plus-strand RNA viruses (1, 24), including the Bamboo mosaic virus (BaMV). In BaMV it has been reported that chloroplast phosphoglycerate kinase (PGK) (25) and HSP90 (Huang et al., unpublished data) are required for the efficient accumulation of BaMV; where as the identity of the additional factors associated within the BaMV RdRp complex, and the proteins involved in satBaMV RNA replication are not yet been acknowledged. This study identified a host metabolic enzyme namely GAPDH, that interact to negatively regulate the Bamboo mosaic virus (BaMV) and its associated satellite RNA accumulation. The RNA binding properties of GAPDH has already been documented for a number of viruses (9, 14, 29, 41, 53, 56). However, the interaction of GAPDH protein with different viral RNAs results in a functionally different mode of regulation on viral replication and translation. For instance: GAPDH int eracts with the JEV NS5 protein indirectly by binding with 3†²-ends of JEV, resulting in virus-induced redistribution of GAPDH to control the early stage of JEV replication/translation (53). GAPDH plays a major functional role in the replication of tombusviruses through the retention of the viral minus-strand RNA template in the replication complex in order to promote asymmetric RNA synthesis (48). In contrast, GAPDH inhibits viral replication in the interaction with other viruses. For example: Silencing GAPDH increases TGEV infection by 2-3 times, demonstrating the anti-TGEV activity of this protein (14). Binding GAPDH to the HAV RNA suppresses cap-independent translation due the destabilization of the secondary structure of RNA (55). In our study, a downregulation of GAPDH-C led to a 2 to 3-fold increase in the replication BaMV and satBaMV RNA, indicating that GAPDH-C has an inhibitory effect on BaMV and satBaMV infection. In addition, an increase in BaMV-GFP was observed on inoculated leaves in GAPDH-C silenced N. benthamiana, revealing that GAPDH-C functions in the early stages while the virus is establishing a successful infection of the primary invaded cells. Similarly, when GAPDH-C is transiently expressed, a 70-80% reduction in the accumulation of BaMV as well a considerable downregulation of BaMV-GFP/satBaMV-GFP was observed in N. benthamiana plants. A similar decrease in the accumulation TMV and the size rather than the number of TMV- GFP foci was observed when TARF was transiently expressed in N. benthamiana (52). Together, this appears to imply that the expression of GAPDH-C has a negative effect on BaMV/satBaMV infection.