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TECHNICAL SESSION: Antiviral defense mechanisms

Dissecting the molecular basis of strain- and temperature-sensitivity to PVY conferred by the potato Nytbr resistance gene
Dennis Halterman - USDA ARS. Rawnaq Chowdhury- University of Wisconsin-Madison, Hari Karki- USDA/ARS, Aurelie Rakotondrafara- University of Wisconsin - Madison

Potato Virus Y (PVY) is one of the most important plant viruses affecting potato production and enters in the list of the top 10 plant viruses in molecular plant pathology. Here we have investigated the nature of Nytbr-mediated resistance against PVY in potato (Solanum tuberosum). The Nytbr gene is strain specific against the common PVYObut not the necrotic strains, and we established its sensitivity to increased temperature. While effective in controlling PVYO at 21?C, elevated growth temperature was sufficient to trigger systemic spread of PVYOthroughout of the Nytbr-bearing potatoes. To shed light on the interplay of elevated temperature and susceptibility, we dissected the earlier step of viral infection in both Nytbr-bearing cultivar Premier Russet (PR) and PVY-susceptible plants. We established that the PVYOhelper component proteinase (HCPro) alone was sufficient to induce a hypersensitive cell death response in PR plants. Remarkably, cell death was enhanced at 28?C, suggesting that at elevated temperature, the HR cell death was not sufficient for restraining PVYO, and other defenses may have been compromised. We uncovered that the production of callose was part of the Nytbr-mediated response and occurs at a very earlier time point in the signal cascade prior to the appearance of local necrosis. Callose accumulation upon viral infection was delayed up to 24 hours at elevated temperature. We propose that callose deposition is a key component of the Nytbr-resistance response and may also be a target of virulent necrotic PVY strains.