Cucumber mosaic virus RNA replicase is essential for systemic infection in Brassica juncea

Background: Brassica juncea belongs to the Brassicaceae family and is used as both an oilseed and vegetable crop. As only a few studies have reported on the cucumber mosaic virus (CMV) in B. juncea , we conducted this study to fill this gap. Methods CMV-Co6, for which systemic infection was confirmed in B. juncea and non-infectious CMV-Rs1 were used. To identify the determinants of systemic infection in B. juncea , we first constructed infectious clones of CMV-Co6 and CMV-Rs1 and used them as pseudorecombinants. Subsequently, the amino acids of the 2a and 2b proteins were compared, and a chimeric clone was constructed. Results RNA2 of CMV was identified as an important determinant in B. juncea because B. juncea were systemically infected with RNA2-containing pseudorecombinants, CMV-Co6, R/6/R, and R/6/6, were systemically infected B. juncea . The chimeric virus R/6Rns/R6cp, in which the C-terminal region of the 2a protein of CMV-Co6 is replaced by CMV-Rs1, still infects B. juncea . Conclusions It is the 2a protein that determines the systemic CMV infection in B. juncea , suggesting that conserved 160G and 214A play a role in systemic CMV infection in B. juncea .