Abstract

Virus Induced gene silencing (VIGS) is a manifestation of RNA silencing pathway, used as a defense response by plant against invading viruses. The first step aimed to develop a VIGS vector for rice based on RTBV to down-regulate endogenous rice genes which was used to silence an endogenous marker gene, phytoene desaturase (pds) in rice plants. The vector is based on binary plasmid and can be easily introduced into rice plants by Agrobacterium-mediated gene transfer. As a counter defense against the VIGS pathway most viruses have developed ways in which they can suppress the silencing pathway. Viral proteins have evolved to block the VIGS pathway for its survival in the host plants. RTBV genome was screened for the presence of any such viral suppressors using GFP expression reversal assay. The experiments to detect suppressor genes in RTBV remained inconclusive. A putative negative element was earlier identified in the RTBV promoter. An attempt was made to further characterize the negative element which was found to be responsible for the repression of transcription of variety of promoters in both monocots and dicot systems in a position- and orientation independent manner.