Umbravirus Gene Expression Helps Potato leafroll virus to Invade Mesophyll Tissues and to be Transmitted Mechanically between Plants

Abstract

Potato leafroll virus (PLRV) was mechanically transmissible when inocula also contained the umbravirus Pea enation mosaic virus-2 (PEMV-2). In plants infected with PLRV and PEMV-2, PLRV accumulated in clusters of mesophyll cells in both inoculated and systemically infected leaves. No transmissions were obtained by coinoculation with Potato virus Y, Potato virus X (PVX), Tobacco mosaic virus, or Cucumber mosaic virus (CMV), although PLRV was transmissible from mixtures with CMV(ORF4) (a recombinant that contained the movement protein (MP) gene of the umbravirus Groundnut rosette virus (GRV) in place of the CMV MP gene). In contrast, neither a recombinant PVX that expressed GRV MP nor a mutant of CMV(ORF4), in which the CMV 2b gene was untranslatable, was able to help PLRV transmission. Possibly both a cell-to-cell movement function and counterdefense mechanisms such as those that block posttranscriptional gene silencing are involved in movement of PLRV within plants and its mechanical transmission between plants.

RNAi-mediated viral immunity requires amplification of virus-derived siRNAs in Arabidopsis thaliana

“…The 2b-deletion mutant of CMV used in this study, CMVf-Δ2b, was from the Fny strain of CMV, a subgroup I strain of CMV (30,31). Unlike the Q strain used previously (13), Fny-CMV induces clearly visible disease symptoms ( Fig.…”

Interaction of a plant virus-encoded protein with the major nucleolar protein fibrillarin is required for systemic virus infection

“…GRV-YB was maintained as a stock isolate. The PEMV-2 cDNA clone was described by Ryabov et al (29). TMV(ORF3-His) expressing His-tagged ORF3 protein was described (16).…”

A cucumber mosaic virus mutant lacking the 2b counter-defence protein gene provides protection against wild-type strains

“…xanthi-nc and xanthi) and Nicotiana benthamiana seeds were germinated in compost and grown in a glasshouse, with supplementary lighting when required. Infectious viral RNA from the subgroup IA CMV strain Fny-CMV (Roossinck & Palukaitis, 1990) and its deletion mutant Fny-CMVD2b was reconstituted by mixing in vitro transcription products of full-length cDNA clones encoding RNA 1 (pFny109), RNA 3 (pFny309), and wild-type RNA 2 (pFny209) or a mutant RNA 2 lacking the 2b open reading frame (ORF) (pFny209/M3), as described previously (Rizzo & Palukaitis, 1990;Ryabov et al, 2001;Soards et al, 2002). Equal volumes of transcripts were combined and gently rubbed with a frosted microscope slide onto tobacco leaves at the three-to-five leaf stage.…”

“…RT-PCR was used to detect, and distinguish between, the RNAs 2 of wild-type Fny-CMV and Fny-CMVD2b occurring in plant RNA samples. The primers were designed to amplify a region of RNA 2 sequence (nt 2367-3031) flanking the 2b ORF of wild-type Fny-CMV as well as the corresponding region in the RNA 2 of Fny-CMVD2b containing a deletion in the 2b ORF (Ryabov et al, 2001) (Fig. 1a).…”

“…This riboprobe, which has been described previously (Carr et al, 1994;Gal-On et al, 1994), can act as a 'general' probe capable of detecting the presence of both wild-type Fny-CMV RNAs and the mutant CMV RNA 2 component of CMVD2b. The second riboprobe was designed to bind specifically to a region of sequence within the 2b ORF to detect the presence of wild-type RNA 2 but not the mutant RNA 2 of CMVD2b, which contains a deletion in this region (Ryabov et al, 2001;Soards et al, 2002). This probe was synthesized by in vitro transcription of a DNA template generated by PCR from wild-type Fny-CMV RNA 2 cDNA sequence using the primers CMV2B.F (59-GAACGAGGTCACAAAAGTCC-39) and CMV2.R_T7 (59-TAATAC-GACTCACTATAGGGAGACGTCAAAATCATGGTCTTCC-39).…”