Abstract
Maize rough dwarf disease (MRDD), caused by several Fijiviruses in the family Reoviridae, is a global disease that is responsible for substantial yield losses in maize. Although some maize germplasm have low levels of polygenic resistance to MRDD, highly resistant cultivated varieties are not available for agronomic field production in China. In this work, we have generated transgenic maize lines that constitutively express rnc70, a mutant E. coli dsRNA-specific endoribonuclease gene. Transgenic lines were propagated and screened under field conditions for 12 generations. During three years of evaluations, two transgenic lines and their progeny were challenged with Rice black-streaked dwarf virus (RBSDV), the causal agent of MRDD in China, and these plants exhibited reduced levels of disease severity. In two normal years of MRDD abundance, both lines were more resistant than non-transgenic plants. Even in the most serious MRDD year, six out of seven progeny from one line were resistant, whereas non-transgenic plants were highly susceptible. Molecular approaches in the T12 generation revealed that the rnc70 transgene was integrated and expressed stably in transgenic lines. Under artificial conditions permitting heavy virus inoculation, the T12 progeny of two highly resistant lines had a reduced incidence of MRDD and accumulation of RBSDV in infected plants. In addition, we confirmed that the RNC70 protein could bind directly to RBSDV dsRNA in vitro. Overall, our data show that RNC70-mediated resistance in transgenic maize can provide efficient protection against dsRNA virus infection.
Highlights
Maize is a very important global resource for human food and animal fodder, and is a key bioenergy source
We demonstrate that two RNC70 transgenic maize lines recovered after more than ten generations of self-crossing and selection have high levels of resistance to maize rough dwarf disease (MRDD) caused by Rice black-streaked dwarf virus (RBSDV)
RBSDV genomic RNA is composed of 10 double-stranded RNAs that might be potential substrates for RNase III
Summary
Maize is a very important global resource for human food and animal fodder, and is a key bioenergy source. The world production of maize was 844.4 million tonnes in 2010 and maize provides the second highest level of production of all food and agricultural commodities (FAO, http://faostat.fao.org/). Several diseases affect maize production, and in China, maize rough dwarf disease (MRDD) complexes contribute substantially to yield losses. The first report of MRDD in China was in 1954 [1], and numerous reports have appeared in different areas since the initial description. In the past few years, disastrous losses caused by MRDD have occurred in most maize growing districts of China. In Shandong province in 2008, the affected area comprised more than 733,000 hm, where 59,100
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