Roles of salicylic acid biosynthesis-pathway in plant virus resistance and pathogenesis in tobacco models
Breeding for plant virus resistance is a potent strategy for crop protection against virus diseases. However, a thorough understanding of the mechanism underlying plant virus resistance and pathogenesis will underpin crop protection. This study elucidates the roles of salicylic acid (SA) biosynthesis-pathway in plant virus resistance and pathogenesis in two tobacco models: inducible chlorosis model system (ihp-HSP90C without the involvement of pathogen molecule) and in the presence of pathogen molecule. This study has established that Nt-n’ is a true allele of N’ gene expressed in wild-type virus-susceptible tobacco. In this study, CRISPR/Cas9-mediated genome editing technology was employed to remove the partial duplication and restore the functional N’ gene in wild-type allotetraploid tobacco (Nicotiana tabacum). Plants with restored and functional N’ gene exhibited robust resistance to ToMV. The expression of nahG (gene encoding SA degrading enzyme, salicylate hydroxylase) alongside the induction of HSP90C-silencing stochastically alleviated chlorosis. nahG expression in virus-resistance tobacco background compromised N’-mediated resistance to ToMV. Application of tenoxicam, an inhibitor of the NPR1-dependent SA signaling pathway upon silencing of HSP90C in the transgenic tobacco, resulted in alleviation of chlorosis and cell death by the suppression of NtSARD1B. The simultaneous knockdown of SA-biosynthesis pathway transcription factor genes, NtSARD1A and NtSARD1B compromised N’-mediated resistance to ToMV resulting in the manifestation of expanded local necrotic lesions and systemic spread of the virus. Collectively, these results suggest that NtSARD1A and NtSARD1B have positive roles in local resistance and systemic acquired resistance to virus infection in tobacco.
