Post-transcriptional gene silencing and its implication to the asian soybean rust- a review article

Soybean is one of the most economically important crops in the world. Soybean yield is severely affected by biotic agents, especially by Asian Soybean Rust (ASR). The causal agent of ASR is Phakopsora pachyrhizi; a biotrophic fungus that belongs to Basidiomycota. Chemical control is the most effective control method for ASR, but it is costly. In the past, many soybean varieties resistant to ASR have been developed by introgression of resistance genes (R genes) to local varieties. Since P. pachyrhizi isolates are highly diverse, the resistant varieties are vulnerable to newly evolved pathogen isolates. Until now there is no variety that is resistant to all pathogen isolates. Therefore, there is a need to develop new strategies other than R genes. Identification of new candidate genes that are crucial for fungi in pathogenicity may lead to new options for P. pachyrhizi control. Many interesting genes have been identified but their study is impaired by the biotrophic nature of rust fungi. In this regard RNAi has emerged as a reverse genetic tool. The HIGS method (Host Induced Gene Silencing) is used to down regulate fungal candidate genes in planta. This is an indirect method where the silencing signal is formed in the plant but it mediates RNAi in the fungus.