Differential Interactions of Bamboo Mosaic Potexvirus Satellite RNAs, Helper Virus, and Host Plants

Abstract

Bamboo mosaic potexvirus (BaMV) supports the replication and encapsidation of a single-stranded satellite RNA (satBaMV). Full-length infectious cDNA clones of sat-BaMV variants with a 0.7 to 7.5% difference in nucleotide sequence were constructed, and in vitro transcripts were co-inoculated with BaMV RNA to barley protoplasts. Co-inoculation with BSL6 satBaMV transcripts resulted in a greatly reduced accumulation of genomic and subgenomic RNAs whereas co-inoculation with the prototype BSF4 or other variants did not. satBaMV variant BSL6-mediated interference occurred at the genomic RNA, subgenomic RNA, and capsid protein levels whereas the synthesis of minus strand was not significantly affected. Attenuation of the BaMV symptoms also was observed in Chenopodium quinoa and Nicotiana benthamiana plants co-inoculated with BSL6 satBaMV. In protoplasts of barley and N. benthamiana, BSF4 and BSL6 variants replicated at a similar level whereas in the inoculated leaves of C. quinoa and N. benthamiana BSL6 accumulated to a much lower level than BSF4, and was encapsidated. BSL6 satBaMV was rarely detected in the systemic leaves of N. benthami-ana co-inoculated with BaMV RNA, indicating that BSL6 satBaMV may be a movement-inefficient variant. It is suggested that this variant may provide a potential source for both resistance against BaMV and insights into the interactions of satellite RNA, helper virus, and symptom expression.