Induction of HSP70 and polyubiquitin expression associated with plant virus replication

Abstract

By examining the front of virus invasion in immature pea embryos infected with pea seed-borne mosaic virus (PSbMV), the selective control of different host genes has been observed. From our observations, the early responses to PSbMV replication can be grouped into three classes, inhibited host gene expression, induced host gene expression, and no effect on a normal host function. The expression of two heat-inducible genes encoding HSP70 and polyubiquitin was induced coordinately with the onset of virus replication and the down-regulation of two other genes encoding lipoxygenase and heat shock cognate protein. The down-regulation was part of a general suppression of host gene expression that may be achieved through the degradation of host transcripts. We discuss the possibilities of whether the induction of HSP70 and polyubiquitin genes represents a requirement for the respective protein products by the virus or is merely a consequence of the depletion of other host transcripts. The former is feasible, as the induction of both genes does result in increased HSP70 and ubiquitin accumulation. This also indicates that, in contrast to some animal virus infections, there is not a general inhibition of translation of host mRNAs following PSbMV infection. This selective control of host gene expression was observed in all cell types of the embryo and identifies mechanisms of cellular disruption that could act as triggers for symptom expression.For maximum efficiency, a virus must balance the exploitation of host cellular processes against consequential cellular damage. How this is achieved is not well understood. However, examples from a wide range of animal viruses (reviewed in ref. 1) and our earlier work with the plant virus pea seed-borne mosaic virus (PSbMV; ref.2) suggest that a major component in the control exerted by the virus is the shutoff of transcription and͞or translation of host mRNAs. Because the virus must use the host machinery for polynucleotide and protein synthesis, either the control must be highly selective or virus replication must depend on long-lived host mRNAs and͞or proteins. A similar argument may also apply to the use of host processes for the correct folding and turnover of viral proteins.The host shutoff phenomenon has been studied in most detail for poliovirus in which viral proteins interfere with DNA polymerase I, II, and III transcription (3-5) and translation (6, 7) and for herpes simplex virus 1 in which host translation is inhibited and there is a rapid degradation of capped mRNAs by a viral protein with riboexonuclease activity (8). For PSbMV replicating in pea embryonic tissues, there is a transient host shutoff associated with a loss of host gene transcripts associated with diverse areas of metabolism (2).In common with all viruses, PSbMV replication is associated with the translation of viral RNA and the multifarious activities of virus-encoded proteins. Hence, the basic translational machinery and processes required to assist in the correct folding and turnover of prote...

Virus Induction of Heat Shock Protein 70 Reflects a General Response to Protein Accumulation in the Plant Cytosol

“…We and others have reported the induction of HSP70 by a wide range of viruses in diverse host plants, including pea (Pisum sativum), N. benthamiana, squash (Cucurbita pepo), tobacco (Nicotiana tabacum), and Arabidopsis (Aranda et al, 1996;Escaler et al, 2000;Havelda and Maule, 2000;Jockusch et al, 2001;Whitham et al, 2003). Based on the differential induction of heat-inducible genes Figure 3.…”

“…those showing high levels of virus replication and viral genome expression) accumulate HSP70 mRNA and protein (Aranda et al, 1996;Escaler et al, 2000). This phenomenon applies to infections with a diverse range of viruses, including members from the Potyvirus, Tobravirus, Potexvirus, Geminivirus (Aranda et al, 1996;Escaler et al, 2000), and Cucumovirus (Havelda and Maule, 2000) genera. While the detailed mechanism of HSP70 induction by plant viruses has not been investigated, for animal viruses specific viral proteins have been shown to be active (Aranda and Maule, 1998, and refs.…”

“…therein). From studies of potyvirus induction of heatinducible proteins (Aranda et al, 1996), however, it seems that the processes of heat and virus induction of HSPs are different.…”

Characterization of a wheat HSP70 gene and its expression in response to stripe rust infection and abiotic stresses

“…In plants, it was reported that HSP70 and HSP90 are essential components in the INF1-mediated hypersensitive response in Nicotiana benthamiana, and that they function upstream or independent of the MAPK cascade [23]. Moreover, various reports describe that HSP70 expression in plants is induced upon infection with pathogens [23][24][25][26], but more detailed analysis of HSP70 expression profiles during plant-pathogen interactions are scarce.…”

The Cytosolic Protein Response as a Subcomponent of the Wider Heat Shock Response inArabidopsis

“…The samples were first subjected to RT-PCR to confirm the virus infection and then subjected to qRT-PCR to quantify the expression level of HSFs. The CPR response associated with virus infection is highly localized, being focused on cells actively involved in virus multiplication and virus and virus genome expression (Aranda et al, 1996). As such, the level of induction of HSFs was less than observed in response to AZC or heat shock.…”