Enhanced Virus Resistance in Transgenic Maize Expressing a dsRNA-Specific Endoribonuclease Gene from E. coli

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.

The Genetics and Genomics of Virus Resistance in Maize

“…In addition, maize expressing an E. coli ribonuclease specific for double-stranded RNA had increased resistance to RBSDV (Cao et al 2013).…”

Control of Virus Diseases in Maize

“…Natural infection, evaluated in disease nurseries or "hot spots" where the disease was naturally endemic or prevalent, was among the early approaches used (Findley et al, 1976). This method continues to be effective for identifying virus-resistant germplasm and characterizing resistance genes and QTLs in maize (Cao et al, 2013;Di Renzo et al, 2004, Ming et al, 1997. However, this approach does not ensure gain under selection, because of unequal disease pressure from season to season and the high risk of escapes.…”

“…Interestingly, transgenic plants expressing SCMV (MDMV-B) were resistant to that virus, but also had pleiotropic resistance to MCMV (Murry et al, 1993). Further, transgenic maize expressing a bacterial dsRNAspecific nuclease (RNAse III) was resistant to RBSDV (Cao et al, 2013), but it is not yet known if this line is resistant to multiple viruses. The MSV-expressing transgenic maize are still being tested in confined field trials (Tomson & Shepherd, 2010), and lines expressing the MDMV P1 provided some virus resistance in the field .…”

Small RNA Based Genetic Engineering for Plant Viral Resistance: Application in Crop Protection

“…Since, ACMV is a DNA virus and its gene expression takes place on viral mini-chromosome structure, viral resistant transgenic cassava was also obtained using hairpin RNA construct targeting the viral promoter for transcriptional gene silencing (hp-TGS) (Vanderschuren et al, 2007). Though, the effectiveness of the transgenic viral resistance has been tested in field trial for many generations (Shimizu et al, 2011; Cao et al, 2013; Wang et al, 2016), currently no SRGE based staple food crop was reported for commercial release.…”