Abstract

The 2b counter-defense protein of cucumber mosaic virus (CMV) disrupts plant anti-viral mechanisms mediated by RNA silencing and salicylic acid (SA). Biosynthesis of SA increased sharply in susceptible plants infected with CMV , a phenomenon usually associated with plant resistance to pathogens. However, SA biosynthesis was not elicited in plants infected with the 2b gene deletion mutant CMV ∆2b, or in plants constitutively expressing the 2b protein. JA levels were unaffected by either CMV or CMV ∆2b. Microarray data gathered in our lab showed that the 2b protein inhibited changes in the expression of 90% of the many genes regulated by jasmonic acid but had few effects on SA-regulated gene expression. JA is an important signal in defense against insects and certain microbes but not against viruses. Our findings suggest that the 2b protein has evolved to modify not only SA-mediated antiviral signaling, but also to disrupt JA-mediated defenses.