Abstract
This study investigated phenotypic responses of Nicotiana benthamiana accessions LAB (RNA-dependent RNA polymerase 1 gene mutant-NbRdRp1m) and MtA-6 (wild-type NbRdRp1), and their F1 hybrids (NbRdRp1/1m) following infection with yellow tailflower mild mottle virus (YTMMV). PCR analysis revealed distinct NbRdRp1 allele sizes in LAB (larger) and MtA-6 (smaller), with F1 hybrids displaying heterozygosity at the NbRdRp1 locus. Symptom severity at 20 days post-inoculation (dpi) with YTMMV showed that LAB plants exhibited severe disease symptoms and high mortality, while MtA-6 and F1 hybrids exhibited moderate symptoms with increased survival rates. F1 hybrids displayed a transient increase in viral RNA at 10 dpi, which decreased by 20 dpi, suggesting a stronger early systemic response compared to the parental lines. Expression analysis of NbRdRp1 and NbRdRp6 revealed the highest expression levels in the F1 hybrids, with significant differences in the NbRdRp1/NbRdRp6 ratio between accessions. Expression of Argonaute (Ago) and small RNA degrading nuclease 1 (SDN1) was also measured, showing distinct patterns of activation, particularly in F1 hybrids, confirming RNA silencing pathways in viral defense. Genotyping of F2 hybrids confirmed the inheritance of both wild type and mutant NbRdRp1 alleles, though viral RNA accumulation did not correlate directly with genotype, highlighting the role of as yet unknown genes in response to YTMMV. These findings underscore the genetic interactions underlying viral resistance in N. benthamiana and emphasize the role of RNA silencing.
