Sense- and antisense-mediated resistance against Sri Lankan cassava mosaic virus (SLCMV) in Nicotiana benthamiana

Abstract

Sri Lankan cassava mosaic virus (SLCMV) is the principal causal agent of cassava mosaic disease in the Indian subcontinent. To gain resistance against the virus, the coat protein (CP) gene, namely the AV1 of SLCMV-Adivaram isolate, was cloned in either sense or antisense orientation under the Cauliflower mosaic virus 35S promoter, and transgenic Nicotiana benthamiana plants were obtained through Agrobacterium-mediated transformation. A total of eight T1 transgenic lines, four harboring the CP-sense construct and four harboring the CP-antisense construct were challenged with agro-infectious clones of SLCMV DNA-A and DNA-B. Based on symptom exhibition at 20 days post inoculation, 3 out of the 4 CP-sense transgenic lines and all 4 CP-antisense transgenic lines showed a high level of resistance against SLCMV. In addition, a delay in symptom initiation was observed in all the transgenic lines inoculated with a high viral load at agro-dilution 1:625 from an absorbance (A600) of 1. However, the resistance was more prominent at a lower viral load of 1:1000 agro-dilution. The viral titer was lower in the SLCMV-challenged transgenic lines compared to the non-transgenic N. benthamiana plants as confirmed by quantitative PCR and dot blot analysis. Furthermore, small RNA Northern blot analysis revealed lowered amounts of virus-specific small interfering RNAs in the resistant transgenic lines as compared to the non-transgenic plants upon SLCMV infection, which correlates to lower virus titers due to resistance against the virus.

Keywords

• coat protein gene
• rnai
• rna silencing
• vsirnas