Transgenic wheat harboring an RNAi element confers dual resistance against synergistically interacting wheat streak mosaic virus and triticum mosaic virus

Authors: Tatineni, Satyanarayana - Ts; SATO, SHIRLEY - University Of Nebraska; NERSESIAN, NATALYA - University Of Nebraska; Alexander, Jeffrey; QUACH, TRUYEN - University Of Nebraska; GRAYBOSCH, ROBERT - Retired ARS Employee; CLEMENTE, THOMAS - University Of Nebraska

Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2019
Publication Date: 1/2/2020
Citation: Tatineni, S., Sato, S., Nersesian, N., Alexander, J.A., Quach, T., Graybosch, R.A., Clemente, T.E. 2020. Transgenic wheat harboring an RNAi element confers dual resistance against synergistically interacting wheat streak mosaic virus and triticum mosaic virus. Molecular Plant-Microbe Interactions. 33(1):108-122. https://doi.org/10.1094/MPMI-10-19-0275-R.
DOI: https://doi.org/10.1094/MPMI-10-19-0275-R

Interpretive Summary: Wheat streak mosaic disease complex, caused by Wheat streak mosaic virus (WSMV), Triticum mosaic virus (TriMV), and High Plains virus, is the most economically important viral disease of wheat in the Great Plains. Since all three viruses are transmitted by the wheat curl mite, mixed infections in combination of any two or all three viruses have been reported in growers’ fields with reduced yield. WSMV and TriMV synergistically interact in co-infected wheat with increased accumulation of both viruses and with enhanced disease severity. Hence, wheat cultivars with resistance to at least two of the three mite-transmitted viruses would minimize yield loss. In this study, transgenic wheat lines were developed by inserting a hairpin RNA element consisting of part of NIb gene sequence of WSMV and TriMV. The transgenic wheat lines had dual resistance to both WSMV and TriMV at 25°C or above. However, the transgenic wheat lines were susceptible to WSMV and TriMV at 20°C, but both viruses accumulated at significantly lower levels compared to those in nontransgenic wheat. The availability of transgenic wheat lines in this study would facilitate stacking the low temperature-sensitive transgene with high temperature-sensitive Wsm1 or Wsm2 genes to obtain wheat cultivars with dual resistance at a wide range of temperatures.

Technical Abstract: Wheat streak mosaic virus (WSMV) and triticum mosaic virus (TriMV) are economically important viruses of wheat, causing significant yield losses in the Great Plains region of the USA. These two viruses are transmitted by wheat curl mites, which often leads to mixed infections with synergistic interaction in growers’ fields that exacerbates yield losses. Thus, development of dual resistant wheat could provide effective control of these two wheat curl mite-transmitted viruses. In this study, a genetic resistance strategy, employing an RNA interference (RNAi) approach, was implemented by assembling a hairpin element composed of a 202-bp stem sequence of the NIb (replicase) gene, from each of WSMV and TriMV in tandem coupled with an intron sequence in the loop. The derived RNAi element was cloned into a binary vector between the maize ubiquitin promoter and nopaline synthase terminator. The resultant plasmid was used to transform spring wheat genotype CB037. Phenotyping of T1 lineages across eight independent transgenic events for resistance revealed that two of the transgenic events provided resistance to WSMV and TriMV, and four events provided resistance to either WSMV or TriMV, and no resistance was found in two of the events. T2 populations derived from the two events, classified as dual resistant, were subsequently monitored for stability of the resistance phenotype through the T4 generation. The resistance phenotype in these events was temperature dependent, with a complete dual resistance at temperatures =25°C and increasingly susceptible response at temperatures below 25°C. Northern blot hybridization of total RNA from transgenic wheat revealed that virus-specific small RNAs (vsRNAs) accumulated progressively with increase in temperature with no detectable levels of vsRNAs accumulation at 20°C. Thus, the resistance phenotype of wheat harboring RNAi element was correlated with accumulation of vsRNAs, and generation of vsRNAs provides molecular markers for the prediction of resistant phenotype of transgenic plants at a specific temperature.