A Distinct, Non-Virion Plant Virus Movement Protein Encoded by a Crinivirus Essential for Systemic Infection

Abstract

Plant viruses encode specific proteins that facilitate their ability to establish multicellular/systemic infections in their host plants. Relatively little is known of the transport mechanisms for plant viruses whose infections are phloem limited, including those of the family Closteroviridae. These viruses have complex, long filamentous virions that spread through the phloem. Lettuce infectious yellows virus (LIYV) encodes a non-virion protein, P26, which forms plasmalemma deposits over plasmodesmata pit fields, and LIYV virions are consistently found attached to those deposits. Here we demonstrate that P26 is a unique movement protein required for LIYV systemic infection in plants. LIYV P26 shows no sequence similarities to other proteins, but other criniviruses encode P26 orthologs. However, these failed to complement movement of LIYV P26 mutants.

ICTV Virus Taxonomy Profile: Closteroviridae

“…Downstream ORFs form a conserved five-gene module encoding a 6K small hydrophobic protein, HSP70h, a ~60 kDa protein, CP and CPm [ 1 ]. Genome expression involves proteolytic processing of the polyprotein encoded by ORF1a; a +1 ribosomal frameshift for the expression of the RdRP domain of ORF1b; downstream ORFs expressed via nested 3′ co-terminal sub-genomic mRNAs (sgmRNAs) [ 2, 3 ].…”

A Review on Viruses Infecting Taro (Colocasia esculenta (L.) Schott)

“…A successful viral infection usually occurs due to the viral genome containing ORFs that could encode the proteins that are necessary for host infections [56]. The genome structure of the viruses in this review encodes putative proteins that are essential in the establishment of a positive infection [5,19,33,47,48].…”

“…The genome structure of the viruses in this review encodes putative proteins that are essential in the establishment of a positive infection [5,19,33,47,48]. The majority of the putative proteins are typical across virus families, such as the MP and RT of the TaBV and TaBCHV, where both of the proteins play a major role in transport mechanism and replication of the viral genome inside the host, respectively [5,19,56,57]. Meanwhile, the genome of CBDV and TaVCV are both found to encode for L polymerase, which is highly likely to be responsible for the enzyme catalysing RNA replication in taro [47,48].…”

Nonstructural p26 proteins encoded by the 3’-proximal genes of velariviruses and criniviruses are orthologs

“…The absence of conserved amino acid positions in the p26 alignment suggests high plasticity of these non-structural proteins, which may indicate their involvement in the response of virus systems to rapidly changing environmental conditions. On the other hand, the p26 protein of lettuce infectious yellows virus (LIYV), the type member of the genus Crinivirus, induces specific ultrastructures in the infected cells -conical plasmalemma deposits over plasmadesmata -that are thought to be associated with the vascular transport of the virus [7,14,15]. In support of this, a knockout LIYV p26 mutant proved to be unable to spread systemically in a Nicotiana benthamiana host [15].…”

“…On the other hand, the p26 protein of lettuce infectious yellows virus (LIYV), the type member of the genus Crinivirus, induces specific ultrastructures in the infected cells -conical plasmalemma deposits over plasmadesmata -that are thought to be associated with the vascular transport of the virus [7,14,15]. In support of this, a knockout LIYV p26 mutant proved to be unable to spread systemically in a Nicotiana benthamiana host [15]. Although the Closteroviridae members other than LIYV do not induce plasmalemma deposits, the involvement of crinivirus and velarivirus p26 proteins in systemic transport cannot be excluded and needs to be tested experimentally.…”