Location: Wheat, Sorghum and Forage ResearchTitle: A two amino acid difference in the coat protein of satellite panicum mosaic virus isolates is responsible for differential synergistic interaction with panicum mosaic virus
|Rekalakunta Venka, Chowda Reddy|
|Palmer, Nathan - Nate|
|KOVACS, FRANK - University Of Nebraska|
|YUEN, GARY - University Of Nebraska|
|Mitchell, Robert - Rob|
|Tatineni, Satyanarayana - Ts|
Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/29/2018
Publication Date: 4/1/2019
Publication URL: http://handle.nal.usda.gov/10113/6368720
Citation: Rekalakunta Venka, C., Palmer, N.A., Edme, S.J., Sarath, G., Kovacs, F., Yuen, G., Mitchell, R., Tatineni, S. 2019. A two amino acid difference in the coat protein of satellite panicum mosaic virus isolates is responsible for differential synergistic interaction with panicum mosaic virus. Molecular Plant-Microbe Interactions. 32:479-490. https://doi.org/10.1094/MPMI-09-18-0247-R.
Interpretive Summary: Switchgrass and millets can be co-infected by Panicum mosaic virus (PMV) and its parasite virus, satellite panicum mosaic virus (SPMV). Proso millet is a convenient surrogate host for evaluating viral diseases of switchgrass. Viral infection can significantly affect plant growth, biomass yield and quality. If infection is severe, it can even result in the death of the plant. Virus particles are composed of a proteinaceous exterior (coat protein) which encloses the viral genetic material. Frequently, the amino acid sequence of the viral coat protein can determine the severity of infection. Co-infection with PMV and SPMV can exacerbate plant damage, depending on the source of the viral isolates. In this study, different combinations of PMV and SPMV isolates were used to define the disease responses of millet host plants. SPMV isolated from Kansas (SPMV-KS) was more virulent than one isolated from Texas, SPMV-Type, when co-inoculated with PMV. Two specific amino acids of the coat protein that differed between SPMV-KS and SPMV-Type were responsible for the increased infectivity of SPMV-KS relative to SPMV-Type. Now, the most virulent combinations of PMV and SPMV can be used to define resistance mechanisms in switchgrass and to develop switchgrass germplasm with improved virus resistance.
Technical Abstract: Panicum mosaic virus (PMV) (genus Panicovirus, family Tombusviridae) and its molecular parasite, Satellite panicum mosaic virus (SPMV), synergistically interact in coinfected proso and pearl millet (Panicum miliaceum L.) plants resulting in a severe symptom phenotype. In this study, we examined synergistic interactions between the isolates of PMV and SPMV by using PMV-NE, PMV85, SPMV-KS, and SPMV-Type as interacting partner viruses in different combinations. Coinfection of proso millet plants by PMV-NE and SPMV-KS elicited severe mosaic, chlorosis, stunting, and eventual plant death compared with moderate mosaic, chlorotic streaks, and stunting by PMV85 and SPMV-Type. In reciprocal combinations, coinfection of proso millet by either isolate of PMV with SPMV-KS but not with SPMV-Type elicited severe disease synergism, suggesting that SPMV-KS was the main contributor for efficient synergistic interaction with PMV isolates. Coinfection of proso millet plants by either isolate of PMV and SPMV-KS or SPMV-Type caused increased accumulation of coat protein (CP) and genomic RNA copies of PMV, compared with infections by individual PMV isolates. Additionally, CP and genomic RNA copies of SPMV-KS accumulated at substantially higher levels, compared with SMPV-Type in coinfected proso millet plants with either isolate of PMV. Hybrid viruses between SPMV-KS and SPMV-Type revealed that SPMV isolates harboring a CP fragment with four differing amino acids at positions 18, 35, 59, and 98 were responsible for differential synergistic interactions with PMV in proso millet plants. Mutation of amino acid residues at these positions in different combinations in SPMV-KS, similar to those as in SPMV-Type or vice-versa, revealed that A35 and R98 in SPMV-KS CP play critical roles in enhanced synergistic interactions with PMV isolates. Taken together, these data suggest that the two distinct amino acids at positions 35 and 98 in the CP of SPMV-KS and SPMV-Type are involved in the differential synergistic interactions with the helper viruses.