Citrus psorosis virus movement protein contains an aspartic protease required for autocleavage and the formation of tubule-like structures at plasmodesmata

ROBLES LUNA, GABRIEL; PEÑA, EDUARDO JOSÉ; BORNIEGO, MARÍA BELÉN; HEINLEIN, MANFRED; GARCÍA, MARÍA LAURA

JOURNAL OF VIROLOGY

AMER SOC MICROBIOLOGY

Lugar: ss; Año: 2018

0022-538X

Plant virus cell-to-cell movement is an essential step in viral infections. This process is facilitated by specific virus-encoded movement proteins (MPs), which manipulate the cell wall channels between neighboring cells known as plasmodesmata (PD). Citrus psorosis virus (CPsV) infection in sweet orange involves the formation of tubule-like structures within PD, suggesting that CPsV belongs to "tubule-forming" viruses that encode MPs able to assemble a hollow tubule extending between cells to allow virus movement. Consistent with this hypothesis, we show that the MP of CPsV (MPCPsV) indeed forms tubule-like structures at PD upon transient expression in Nicotiana benthamiana leaves. Tubule formation by MPCPsV depends on its cleavage capacity, mediated by a specific aspartic protease motif present in its primary sequence. A single aminoacid mutation in this motif abolishes MPCPsV cleavage, alters the subcellular localization of the protein and negatively affects its activity in facilitating virus movement. The amino terminal 34 kDa cleavage product (34KCPsV), but not the 20 kDa fragment (20KCPsV), supports virus movement. Moreover, similar to tubule-forming MPs of other viruses, the MPCPsV (and also the 34KCPsV cleavage product) can homo-oligomerize, interact with PD-Located Protein 1 (PDLP1) and assemble tubule-like structures at PD by a mechanism dependent on the secretory pathway. 20KCPsV retains the protease activity and is able to cleave a cleavage-deficient MPCPsVin trans Altogether, these results demonstrate that CPsV movement depends on the autolytic cleavage of MPCPsV by an aspartic protease activity, which removes the 20KCPsV protease and thereby releases the 34KCPsV protein for PDLP1-dependent tubule formation at PD