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

Abstract

Abstract 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.