Plant Molecular Biology Group, International Centre for Genetic Engineering and Biotechnology, Aruna Asaf Ali Marg, New Delhi-110067.
Abstracts of Research Papers Presented during the National Symposium of Indian Virological Society at Unit of Plant Virology, Division of Plant Pathology, Indian Agricultural Research Institute, New Delhi-110 012, October 14–1.
Post transcriptional gene silencing (PTGS), a conserved biologicfal phenomenon, processes double stranded RNA into 21–25 nucleotide RNA fragments that directs ribonucleases to degrade the target mRNAs. PTGS has evolved in plants as a defense mechanism against viruses. During viral infection the replicative intermediates of RNA viruses trigger the RNA silencing in plants. Thus successful virus infection requires evasion or suppression of gene silencing and as a counter defense, many viruses encode proteins that specifically inhibits the silencing machinery of the host plant. Here, we report that a 16kDa protein encoded by the AL2 ORF of the Indian Mungbean Yellow Mosaic Virus (IMYMV) is a potent silencing suppressor that prevents the spreading of mobile silencing signal. To validate the hypothesis that AL2 encoded protein would act as a silencing suppressor, reversal of silencing assay was adopted. During the reversal of silencing assay, the leaves (partially expressing GFP) of GFP transgenic plants were infiltrated with Agrobacterium strain LBA4404 carrying either AL2/pBI121 or FHV-B2/pBI121 (used as positive control) construct, it was observed that the infiltrated zone of the non-expressing GFP leaf was showing bright green fluorescence under UV-light at 8 and 7dpi respectively. In an independent experiment designed to elicit transgene silencing using IMYMV-based VIGS vector, we also observed that the silencing signal was confiend to the infltrated zone only till 15dpi. After 15 days post infiltration, the infiltrated zone showed green fluorescence under UV-light, confirming the reversal of silencing phenomenon elicited by Geminiviral AL2 ORF.
