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POSTERS: Molecular plant-microbe interactions

Net charges at the N-terminus of capsid protein interfere with Potexvirus systemic movement
Zhongguo Xiong - University of Arizona. Shanshan Shi- University of Arizona, Sierra Kaszubinski- University of Arizona, Chunqiang Li- Chinese Academy of Tropical Agricultural Science, Ash Nair- University of Arizona, Daniel Zorba- University of Arizona

Pepino mosaic virus (PepMV) is a member of the Potexvirus genus. The virus has a 6.4 kb single stranded (+)-sense RNA genome, encoding for RNA-dependent RNA polymerase, triple gene block, and capsid protein (CP). PepMV CP is required for both viral cell-to-cell movement via plasmodesmata and systemic movement via phloem. Little is known about the mechanisms of CP’s involvement in viral movement. We engineered a mutant PepMV with seven additional amino acids at the N-terminus of its CP, including three highly positive-charged arginine residues. This N-terminal modification prevented the systemic movement of the recombinant virus but did not affect its cell-to-cell movement. Progeny viruses with restored systemic movement were recovered and found to contain compensatory mutations in the modified N-terminal region of PepMV CP, leading to an overall lower positive charge. We hypothesize that the increased positive charge of the CP N-terminal region interferes with the systemic movement function of PepMV CP. Five additional mutants with various net charges at the CP N-terminus were designed and tested to determine if altered charges caused the impaired systemic movement of PepMV. Our results indicated that increased positive charges at the N-terminus of PepMV CP blocked the systemic movement of the virus, and that the roles of PepMV CP in the cell-to-cell movement and in systemic movement can be uncoupled.