Engineering tungro resistance, sequence analysis and fine mapping of negative promoter element of Rice tungro bacilliform virus
Rice tungro, one of the most economically important viral diseases of rice is caused by simultaneous infection of two dissimilar viruses; Rice tungro bacilliform virus (RTBV), a pararetrovirus with a double-stranded DNA genome and Rice tungro spherical virus (RTSV), a plant picornavirus with a single stranded positive sense RNA genome. In order to study the variability of genome of RTBV isolates, the genome of an RTBV isolate from Kanyakumari was investigated. Comparative analaysis of all the reported full length sequences of RTBV showed that Indian isolate clubbed together as a separate sub-group, being distinctly different from the sequences reported from Southeast Asia. Study of viral promoters has been very useful in developing robust gene expression systems for heterologous genes in organisms. The promoter of RTBV has been reported to drive tissue- and developmental stage-specific gene expression in rice. A negative element (NE) was identified in the downstream region of RTBV promoter. This element was found to down-regulate CaMV35S and Maize ubiquitin promoter and functions in position- and orientation-independent manner. Transgenic resistance against RTBV and RTSV separately has been attempted and some degree of resistance has been reported in certain transgenic lines expressing RNA against RTBV and RTSV.