Functionality of host proteins in Cucumber mosaic virus replication: GAPDH is obligatory to promote interaction between replication-associated proteins.

Here, we evaluated the role of two host proteins, a Bromo domain containing RNA binding protein (BRP1) and Glyceraldehyde 3-phosphate dehydrogenase (GAPDH), in the replication of Cucumber mosaic virus (CMV). LC-MS/MS analysis of host/viral proteins pull down against BRP1 from CMV-infected plants co-infiltrated with BRP1-FLAG agroconstruct identified that BRP1 specifically interacts with a ten amino acid motif (843-SPQDVVPLVR-852) encompassing the helicase domain of replicase protein p1a. The interaction between BRP1 and p1a was subsequently confirmed using a BiFC assay. Among fourteen other host proteins identified to interact with BRP1 during CMV infection, six were found to block accumulation of viral progeny in Arabidopsis thaliana lines defective in each of these host proteins. Additional BiFC assays followed by trans-complementation assays identified that plant lines defective in the expression of GAPDH blocked CMV replication by interfering with p1a:p2a interaction. Distinct roles of BRP1 and GAPDH in the replication of CMV are discussed.