S.45. Molecular characterization of a putative movement protein encoded by ORF 1 of Sesbania mosaic virus
Abstract
The movement proteins are one of the most versatile viral proteins, necessary for intercellular transport of virus within the plant. It was first identified in Tobacco mosaic virus (TMV), and since then the movement proteins of several distinct genera of plant viruses have been characterized and shown to interact with host cytoskeletal elements, the cognate viral genome, and modulate the host intercellular communication to enable virus movement. Sesbania mosaic virus (SeMV), which infects Sesbania grandiflora, is a member of Sobamovirus genus and is transmitted by mechanical inoculation and by thrips. It consists of a single stranded positive sense RNA genome. The ORF-1 of SeMV genome has been proposed to code for a putative movement protein of 19 kDa, which could help in the intercellular spread of the virus. It has very limited homology with movement proteins from other species of Sobamovirus genus, the closest being the movement protein of Rice yellow mottle virus (32% homology). It is a cysteine rich protein having a prominent nucleic acid binding domain at the C terminus. The E.coli expressed ORF-1 protein was purified from inclusion bodies under denaturing conditions and was refolded by stepwise removal of the denaturant. It was observed that the refolded protein binds to single stranded RNA, but is unable to interact with DNA. Ni-NTA pull down assay performed with N-terminal histidine tag ORF-1 protein demonstrated that it interacts with coat protein (ORF-4), it is possible that CP and ORF 1 protein are both required for the intercellular transport of the virus within the host. It was also observed that ORF 1 protein could be phosphorylated by cell wall enriched fractions from Arabidopsis thaliana, Sesbania grandiflora, and Niconia tabacum that may be necessary for the modulation of intercellular viral transport by the host. Thus ORF 1 protein is multifunctional in being able to bind to viral RNA, interact with CP and undergo phosphorylation. Studies are in progress to identify the domains involved in each of these functions.
