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Mapping synergistic interaction determinants between Panicum mosaic virus and Satellite panicum mosaic virus

Satyanarayana Tatineni: USDA-ARS

<div><em>Panicum mosaic virus</em> (PMV; genus <em>Panicovirus</em>; family <em>Tombusviridae</em>) causes mild mosaic symptoms on switchgrass (<em>Panicum virgatum</em>) and other millets. <em>Satellite panicum mosaic virus</em> (SPMV) depends on PMV for its replication and movement. PMV and SPMV synergistically interact in co-infected millets resulting in severe mosaic, yellowing, and stunting of plants. In this study, infectious cDNA clones of a Nebraska isolate of PMV and a Kansas isolate of SPMV (GenBank accession # M17182) were developed. Symptom phenotypes of PMV-NE alone and PMV-NE+SPMV-K were compared with those of PMV-TX alone and PMV-TX+SPMV-TX on proso millet (<em>Panicum miliaceum</em>). Both PMV-TX and NE isolates elicited mild mosaic symptoms. Co-infection of proso millet by PMV-NE+SPMV-K elicited severe mosaic, yellowing, and stunting compared to moderate symptoms by PMV-TX+SPMV-TX, suggesting that either PMV-NE or SPMV-K contributed to the observed robust synergistic interaction in proso millet. Additionally, co-infection of proso millet by PMV-TX or PMV-NE with SPMV-K but not with SPMV-TX elicited severe symptoms, indicating that SMPV-K was the main contributor to efficient synergistic interaction with PMV isolates. Comparison of the genome sequences of SPMV-K and SPMV-TX revealed 11 nucleotide differences with four non-synonymous and three synonymous changes in the coat protein ORF. These genomic differences between SPMV isolates provide the bases for the differential synergistic interaction with PMV.</div>