Abstract

Rice tungro disease is caused by a complex of DNA-RNA virus, namely Rice tungro bacilliform virus (RTBV), a DNA virus and Rice tungro spherical virus (RTSV) a RNA virus. Plant viruses trigger strong RNA silencing response and subsequently the viral genome is targeted by the virus derived siRNA which accumulate to high levels during virus infection. This study focuses on the analysis of small RNA (VsRNA) produced in rice in response to rice tungro infection and is aimed at gaining an insight into the plausible RNAi defence triggered against rice tungro infection and to look at differentially regulated miRNA following infection with RTBV and RTSV. Results showed that RNA silencing response of the complex, RTSV is weaker than RTBV and possibly involves DCL3/DCL2 to generate 24 nt/ 23 nt siRNA and final degradation of the viral RNA. Identification of the targets of the differentially expressed osa-miRNA revealed that rice tungro infection affects gene involved in plant defense, hormone signalling and development pathway. Furthermore the complete RTSV genome was successfully amplified in two parts (PI and PII) with catalase intron and lox sites for the construction of a stable intron-containing infectious cDNA clone. The transcripts of Sri Lankan cassava mosaic virus were mapped using the infected laboratory plant Nicotiana benthamiana