Abstract
Rice (Oryza sativa L.) is cultivated in more than 100 countries and supports nearly half of the world’s population. Developing efficient methods to control rice viruses is thus an urgent necessity because viruses cause serious losses in rice yield. Most rice viruses are transmitted by insect vectors, notably planthoppers and leafhoppers. Viruliferous insect vectors can disperse their viruses over relatively long distances, and eradication of the viruses is very difficult once they become widespread. Exploitation of natural genetic sources of resistance is one of the most effective approaches to protect crops from virus infection; however, only a few naturally occurring rice genes confer resistance against rice viruses. Many investigators are using genetic engineering of rice plants as a potential strategy to control viral diseases. Using viral genes to confer pathogen-derived resistance against crops is a well-established procedure, and the expression of various viral gene products has proved to be effective in preventing or reducing infection by various plant viruses since the 1990s. RNA interference (RNAi), also known as RNA silencing, is one of the most efficient methods to confer resistance against plant viruses on their respective crops. In this article, we review the recent progress, mainly conducted by our research group, in transgenic strategies to confer resistance against tenuiviruses and reoviruses in rice plants. Our findings also illustrate that not all RNAi constructs against viral RNAs are equally effective in preventing virus infection and that it is important to identify the viral “Achilles’ heel” gene to target for RNAi attack when engineering plants.
Highlights
Rice (Oryza sativa L.), one of the most important grain crops, is grown worldwide, with more than 90% (650 million tons) in Asia, where it is consumed directly to supply 36% of the total calories consumed (Normile, 2008; Zeigler and Barclay, 2008)
By analyzing the effects of potential target sequences in each of the coding genes in the Rice dwarf virus (RDV) genome, we found transgenic plants that harbored the RNA interference (RNAi) constructs targeting the genes for Pns6, P8, or Pns12 were completely resistant against the RDV infection, suggesting that these proteins are key components at the early stages of viral proliferation
These results indicated that the Rice grassy stunt virus (RGSV) genes for the nucleocapsid protein and movement protein are the viral “Achilles’ heel” to target for RNAi attack and provided further evidence that targeting these genes are effective in conferring strong resistance against tenuiviruses in transgenic rice plants
Summary
Rice (Oryza sativa L.), one of the most important grain crops, is grown worldwide, with more than 90% (650 million tons) in Asia, where it is consumed directly to supply 36% of the total calories consumed (Normile, 2008; Zeigler and Barclay, 2008). The transgenic rice plants with the introduced RNAi construct targeting the RDV gene for Pns 6 (viroplasm associated protein and movement protein), P8 (major outer capsid), and Pns (viroplasm associated protein) were almost immune to RDV infection. By analyzing the effects of potential target sequences in each of the coding genes in the RDV genome, we found transgenic plants that harbored the RNAi constructs targeting the genes for Pns, P8, or Pns were completely resistant against the RDV infection, suggesting that these proteins are key components at the early stages of viral proliferation. When the plants inhibited the expression of the viral major outer capsid, viroplasm-associated protein and viral movement protein via RNAi, they developed the strongest resistance against RDV infection. Transgenic plants with the introduced RNAi constructs targeting the www.frontiersin.org
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