Banana bunchy top virus (BBTV) is a plant pathogen with a multicomponent single-stranded DNA genome that must be converted to double-stranded form for viral gene expression and replication. This study demonstrates that BBTV virion DNA can self-prime complementary strand synthesis in vitro without exogenous primers. Researchers identified and characterized endogenous DNA primers approximately 80 nucleotides long associated with BBTV virions. These primers, found to be entirely DNA rather than RNA, are heterogeneous in size and map to the major common region (CR-M) of the viral genome with variable 5' initiation sites. Interestingly, most sequenced primers derived from BBTV DNA-5, a component whose protein function remains unknown. Using component-specific probes, five of six BBTV components (DNA-1, 2, 4, 5, and 6) were confirmed capable of self-primed extension, with DNA-5 producing the highest amount of extension products. The findings suggest a mechanism analogous to bacterial plasmid replication, where conserved genome regions may direct primer synthesis through virus-encoded proteins, enabling the initial strand synthesis necessary for viral replication.

Key findings

• BBTV genomic ssDNA contains endogenous DNA primers (~80 nucleotides) that enable self-priming of complementary strand synthesis in vitro
• Primers map to the major common region (CR-M) with variable 5' initiation sites and more conserved 3' termination sites
• Most cloned primers originated from BBTV DNA-5, suggesting this component may play an important early role in infection
• Five of six BBTV components (DNA-1, 2, 4, 5, 6) were capable of self-primed extension; DNA-3 showed no detectable extension
• The CR-M contains conserved structural domains including a G-C rich inverted repeat similar to single-strand initiation signals found in bacterial plasmids