Reversible Change in the Nucleoprotein Composition of Bromoviruses after Multiplication in Chenopodium hybridum L.

This study examined how brome mosaic virus (BMV) and cowpea chlorotic mottle virus (CCMV) change when grown in Chenopodium hybridum plants compared to their standard host plants. When BMV and CCMV were isolated from C. hybridum leaves, they showed significantly altered RNA composition—specifically, reduced amounts of RNA-3 and RNA-4 (by approximately half for BMV and one-third for CCMV) compared to virus from barley and cowpea respectively. This change was independent of infection type (local necrotic, local chlorotic, or systemic) and occurred in both green and purple varieties of C. hybridum. The altered RNA composition correlated with changes in nucleoprotein particle distribution detected by density gradient centrifugation. Importantly, this change was reversible: when virus from C. hybridum was re-propagated in the original host plants (barley for BMV, cowpea for CCMV), the normal RNA and nucleoprotein compositions were restored. The specific infectivity of virus from C. hybridum remained comparable to standard isolates despite the compositional changes. Temperature influenced the extent of RNA alteration, with lower temperatures favoring more RNA-(3+4) encapsidation.

Key findings

• BMV and CCMV showed reversible, host-dependent changes in RNA component composition when grown in C. hybridum, with reduced RNA-3 and RNA-4 proportions compared to standard host plants
• The RNA compositional changes correlated with altered nucleoprotein particle distributions visible in density gradient analysis
• These changes were independent of infection type and occurred in both green and purple C. hybridum varieties
• The changes were reversed when virus was re-propagated in standard host plants, indicating the phenomenon was not a permanent genetic alteration
• Temperature during infection influenced RNA composition, with lower temperatures increasing RNA-(3+4) encapsidation