High-level expression of alternative oxidase protein sequences enhances the spread of viral vectors in resistant and susceptible plants

Abstract

The alternative oxidase (AOX) is the terminal oxidase of the cyanide-resistant alternative respiratory pathway in plants and has been implicated in resistance to viruses. When tobacco mosaic virus (TMV) vectors were used to drive very high levels of expression of either AOX or AOX mutated in its active site (AOX-E), virus spread was enhanced. This was visualized as the induction of larger hypersensitive-response lesions after inoculation onto NN-genotype tobacco than those produced by vectors bearing sequences of comparable length [the green fluorescent protein (gfp) gene sequence or antisense aox] or the 'empty' viral vector. Also, in the highly susceptible host Nicotiana benthamiana, systemic movement of TMV vectors expressing AOX or AOX-E was faster than that of TMV constructs bearing gfp or antisense aox sequences. Notably, in N. benthamiana, TMV.AOX and TMV.AOX-E induced symptoms that were severe and ultimately included cell death, whereas the empty vector, TMV.GFP and the TMV vector expressing antisense aox sequences never induced necrosis. The results show that, if expressed at sufficiently high levels, active and inactive AOX proteins can affect virus spread and symptomology in plants.

Transient Transcriptional Regulation of theCYS-C1Gene and Cyanide Accumulation upon Pathogen Infection in the Plant Immune Response

“…It has been suggested that tobacco and tomato cyanideinduced resistance to virus is mediated by AOX, which would contribute to the signal transduction pathway leading to resistance (Chivasa and Carr, 1998;Fu et al, 2010). Strikingly, when overexpressing either the native AOX or a version of AOX mutated at its active site, tobacco mosaic virus vectors increase systemic movements in Nicotiana benthamiana (Murphy et al, 2004).…”

The reduction of reactive oxygen species formation by mitochondrial alternative respiration in tomato basal defense against TMV infection

“…Accordingly, recent studies have also shown that if plants lacking AOX are environmentally stressed, the damage is greater either in terms of ROS production or cell death (Giraud et al 2008;Watanabe et al 2008). To date, only a few studies have examined the changes in the AOX content in a whole plant challenged with TMV, and all of these have been conducted with tobacco plants (Ordog et al 2002;Gilliland et al 2003;Murphy et al 2004). These previous studies have focused on the involvement of AOX in the anti-TMV defense response using transgenic lines with altered AOX gene expression and alternative-pathway capacity.…”

“…These previous studies have focused on the involvement of AOX in the anti-TMV defense response using transgenic lines with altered AOX gene expression and alternative-pathway capacity. To our knowledge, only Murphy et al (2004) have analyzed the ROS production during this process in tobacco plants. The authors found that increased amounts of H 2 O 2 accumulated not only in AOX-overexpressing lines but also in lines transformed with AOX that carried a mutation in its active site, and they speculated that abnormal levels of AOX proteins could indirectly perturb the AOX-mediated detoxification of ROS in the mitochondria and thus the mitochondrial redox balance.…”

“…5a). H 2 O 2 levels are routinely used as a general marker for ROS production upon infection with TMV (Murphy et al 2004). In our study, a time course (from 1 dpi to the end of the experiment) change of H 2 O 2 levels also confirmed that the leaf H 2 O 2 content was significantly higher in the SHAMpretreated leaves and lower in the KCN-pretreated leaves than those in the plants that are subjected to TMV inoculation only (Fig.…”

The roles of ascorbic acid and glutathione in symptom alleviation to SA-deficient plants infected with RNA viruses

“…However, when Tobacco mosaic virus (TMV) vectors induced a high expression level of alternative oxidase (AOX), the virus spread was faster, and the symptom became more severe, in spite of the virus replication level (Murphy et al 2004). Another example is the TCV-satC (a satellite RNA associated with TCV) system, where symptoms are substantially enhanced and virus levels are signiWcantly reduced (Sun and Simon 2003).…”