Abstract
The satellite RNA of bamboo mosaic virus (satBaMV) has a single open reading frame encoding a non-structural protein, P20, which facilitates long-distance movement of satBaMV in BaMV and satBaMV co-infected plants. Immunohistochemistry and immunoelectron microscopy revealed that the P20 protein accumulated in the cytoplasm and nuclei in co-infected cells. P20 and the helper virus coat protein (CP) were highly similar in their subcellular localization, except that aggregates of BaMV virions were not labelled with anti-P20 serum. The BaMV CP protein was fairly abundant in mesophyll cells, whilst P20 was more frequently detected in mesophyll cells and vascular tissues. The expression kinetics of the P20 protein was similar to but slightly earlier than that of CP in co-infected Bambusa oldhamii protoplasts and Nicotiana benthamiana leaves. However, satBaMV-encoded protein levels declined rapidly in the late phase of co-infection. During co-infection, in addition to the intact P20, a low-molecular-mass polypeptide of 16 kDa was identified as a P20 C-terminally truncated product; the possible method of generation of the truncated protein is discussed.
Highlights
Single-stranded satellite RNAs of plant viruses, ranging from 0.2 to 1.5 kb, are classified on the basis of their coding capacity
Most of the mRNA-type satellite RNAs (satRNAs) are associated with nepoviruses (Roossinck et al, 1992; Fritsch et al, 1993), and their non-structural proteins are indispensable for replication (Hans et al, 1993; Hemmer et al, 1993; Liu & Cooper, 1993). satRNAs without a functional open reading frame (ORF) are 0.2–0.5 kb in size, with highly specialized structures, and are associated with several plant virus groups, including cucumovirus, nepovirus and sobemovirus (Roossinck et al, 1992; Garcia-Arenal & Palukaitis, 1999; Simon et al, 2004)
Our light microscopy analysis of immunostained Bamboo mosaic virus (BaMV) and satellite RNA of bamboo mosaic virus (satBaMV) co-infected bamboo leaves revealed a mosaic-like pattern of BaMV coat protein (CP) and satBaMV P20 expression in epidermal, mesophyll and bundle sheath cells
Summary
Single-stranded satellite RNAs (satRNAs) of plant viruses, ranging from 0.2 to 1.5 kb, are classified on the basis of their coding capacity. Most of the mRNA-type satRNAs are associated with nepoviruses (Roossinck et al, 1992; Fritsch et al, 1993), and their non-structural proteins are indispensable for replication (Hans et al, 1993; Hemmer et al, 1993; Liu & Cooper, 1993). SatRNAs without a functional ORF are 0.2–0.5 kb in size, with highly specialized structures, and are associated with several plant virus groups, including cucumovirus, nepovirus and sobemovirus (Roossinck et al, 1992; Garcia-Arenal & Palukaitis, 1999; Simon et al, 2004). Translation of the satRNA of tomato black ring virus (TBRV) with WGE and RRL
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