Function Analysis Of Rice Stripe Virus Pc4Protein

Rice stripe disease is a kind of severe virus disease, which has caused great losses of riceproduction in our country. However, our knowledge to its pathogen, Rice stripe virus （RSV）, is notenough. RSV is a kind of negative RNA virus, the unusual genome organization and translation strategyhave prevented the development of a cloned genetic system for RSV, making it impossible to directlymanipulate specific genes within the context of viral genomes. Little progress has been made incharacterizing the biological roles of the seven RSV encoded proteins until recent years. The Rice stripevirus pc4has been determined as the viral movement protein （MP）. Whether pc4has other functions, orprecise domain related to it’s function are largely unknown.In this study, the pc4gene was cloned into a movement-deficient Tobacco mosaic virus （TMV）.The resulting hybrid TMVpc4, in addition to spreading cell to cell in Nicotiana tabacum, movedsystemically and induced foliar necrosis in Nicotiana benthamiana, indicating novel functions of theRSV pc4that induces symptom and long distance movement in N. benthamiana. To determinefunctional domain（s） of the RSV pc4protein required for movement and foliar necrosis development,twelve clusters of charged amino acid（s） conserved within identical or highly similar regions of thetenuiviral pc4proteins were selected for alanine-substitution mutagenesis in the RSV isolate used in thisstudy.The systematic alanine-scanning mutagenesis study established the region K¹22–D²58of the pc4substantially associated with cell-to-cell movement, and mutants by replacement of KGR122–124, D135,ED^170–171, ER^201–202, EFE^218–220or ELD⁹256–258)with alanine（s） no longer moved cell to cell. However,only one amino acid group KGR122–124was linked with long-distance movement. The region D17–K33was recognized as a crucial domain for leaf necrosis response, and mutagenesis of DD^17–18or RK^32–33greatly attenuated necrosis. The overall data suggested manifold roles of the pc4during the RSVinfection in its experimental host N. benthamiana.