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.

Structural homology between bamboo mosaic virus and its satellite RNAs in the 5'untranslated region

“…3a), while some disrupt a previously proposed structure in negative-strand RNA (Lin et al, 2005). Strain-specific variations in BaMV may be responsible for differences in gRNA accumulation, symptom induction and satRNA-mediated interaction, as shown previously (Hsu et al, 1998;Yeh et al, 1999). For instance, satBaMV-BSF4 has been shown to promote formation of local lesions on Chenopodium quinoa leaves when co-infected with BaMV-L, a sat-free BaMV derived from BaMV-V which is naturally associated with satRNAs Hsu et al, 1998).…”

“…Several BaMV strains, including BaMV-S, BaMV-O, BaMV-L and BaMV40A, have been isolated or generated in the past and used in studies of BaMV biology and satBaMV-mediated regulation (Chang et al, 1997;Hsu et al, 1998;Chen et al, 2005). We note that none of these strain-specific variations is in conflict with the formation of stem-II in positive-strand RNA (Fig.…”

“…Infections by BaMV are frequently associated with the presence of satellite (sat) RNAs, some of which may reduce accumulation of BaMV RNA and attenuate BaMVinduced symptoms in co-infected plants (Hsu et al, 1998).…”

“…The constructed mutants were verified by DNA sequencing and subsequently used for the synthesis of capped and poly-adenylated transcripts in vitro; the sequence for the poly-A tail is contained within the plasmid. After removing DNA templates, these infectious transcripts were applied to N. benthamiana plants as described by Hsu et al (1998). Briefly, three 1-month-old N. benthamiana plants were used, of which two leaves were inoculated for each inoculation.…”

Mimicry of molecular pretenders: The terminal structures of satellites associated with plant RNA viruses

“…Although the rolling-circle replication of satRPV RNA may have no specific initiation site, similar branched SL structures (Y-shaped) were identified as the putative replicase recognition but BSL6 interfered with genomic RNA, greatly reduced the accumulation of genomic and subgenomic RNA and CP in protoplasts, and attenuated BaMV symptoms in Chenopodium quinoa and Nicotiana benthamiana plants. 62 The secondary structure in the 5' UTR of BSL6 folds into 5 SLs (SL-I to SL-V), as confirmed by enzymatic probing. The apical hairpin SL (AHSL), located in the upper part of SL-III, is involved in the downregulation of BaMV replication (Fig.…”