Viola philippica, a medicinal herbaceous plant documented in the Chinese Pharmacopoeia, is a promising candidate for research into plant-derived pharmaceuticals. However, the study of newly emerging viruses that threaten the cultivation of V. philippica remains limited. In this study, V. philippica plants exhibiting symptoms such as leaf yellowing, mottled leaves, and vein chlorosis were collected and subjected to RNA sequencing to identify potential viral pathogens. A novel polerovirus, named Viola Philippica Polerovirus (VPPV), was identified in V. philippica. VPPV possesses a linear, positive-sense, single-stranded RNA genome consisting of 5535 nucleotides (nt) and encodes seven highly overlapping open reading frames (ORFs). Two potential recombination events were identified within ORF2, ORF3a, and ORF3, providing insights into the genetic diversity and evolution history of this novel polerovirus. An infectious cDNA clone of VPPV was successfully constructed and shown to infect Nicotiana benthamiana. Using a PVX-based heterologous expression system, the VPPV P0 protein was shown to trigger a systemic hypersensitive response (HR)-like reaction in N. benthamiana, indicating that P0 functions as the main pathogenicity determinant. These findings contributed to the detection and understanding of pathogenic mechanisms and control strategies for VPPV in V. philippica.
Keywords: RNA-seq; Viola philippica polerovirus; Violae Herba; hypersensitive response; novel viruses; pathogenicity determinant; recombination.