Investigating a new role for the Cauliflower mosaic virus P6 protein: Delivery of virions to plasmodesmata
J. SCHOELZ (1), C. A. Angel (1), A. Rodriguez (1), S. Leisner (2), R. S. Nelson (3). (1) University of Missouri, Columbia, MO, U.S.A.; (2) University of Toledo, Toledo, OH, U.S.A.; (3) The Samuel Roberts Noble Foundation, Ardmore, OK, U.S.A.
The P6 protein of <i>Cauliflower mosaic virus</i> (CaMV) assembles in the cytoplasm into large, amorphous inclusion bodies (IBs) that associate with and move on microfilaments. The CaMV IBs are considered virion factories, as they are the site for genome amplification and virion assembly. Because the majority of virions are associated with P6 inclusion bodies, we have hypothesized that P6 IBs function to move virus complexes or virions within the cell to the plasmodesmata. A yeast two-hybrid screen of an <i>Arabidopsis</i> cDNA library with CaMV P6 as the bait has identified two proteins that might have distinct roles in intracellular trafficking of CaMV. One Arabidopsis protein identified in the screen is CHUP1 (Chloroplast Unusual Positioning 1), a protein localized to the outer envelope of chloroplasts and is responsible for their movement on actin microfilaments. Transient co-expression of CHUP1 and P6 tagged with fluorescent proteins revealed that CHUP1 and P6 co-localize within the cell. Furthermore, expression of a truncated CHUP1 blocked the movement of P6 IBs. A second protein, C2CDMT, is a calcium-dependent membrane targeting protein with a C2 domain. Transient co-expression studies with C2CDMT with P6 tagged with fluorescent proteins has revealed that some P6 IBs associate with C2CDMT at plasmodesmata. Taken together, these studies indicate that P6 IBs may be able to utilize host proteins for intracellular movement on microfilaments to travel to plasmodesmata.
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