Regulation of the expression of plant defence genes

Abstract

The hypersensitive response of plants to infection by pathogens is associated with the induction of the expression of genes encoding pathogenesis-related (PR) proteins and the development of a systemic acquired resistance of the plant to viruses, fungi and bacteria. The PR genes induced in Samsun NN tobacco mosaic virus (TMV) have been classified into five groups, each encoding acidic extracellular and basic vacuolar proteins. In addition to induction by TMV, many PR genes are induced by treating the plant with salicylic acid (SA). Genes encoding acidic PRs are systemically induced upon TMV infection whereas genes encoding basic PRs are not. In contrast to the genes encoding acidic PRs, the genes encoding basic PRs are induced by ethylene and wounding. Cis-acting regulatory elements involved in the co-ordinate induction of PR genes by TMV and SA have been mapped in most detail in the PR-la promoter. This promoter contains a number of elements that bind a GT-1 like transcription factor with different affinities. To study the role of ethylene in the induction of PR gene expression, plants have been transformed with sense and antisense constructs of tobacco cDNAs encoding ACC-synthase and/or ACC-oxidase.

Genotype-dependent expression of specific members of potato protease inhibitor gene families in different tissues and in response to wounding and nematode infection

“…When compared to Desirée, P40 showed a stronger but delayed response, similar as observed for the PKPI group A and PI-1 family transcripts. As expected, the wound treatment did not cause changes in the relative abundance of PR1 transcripts (not shown), since wounding does not affect the salicylic acid response pathway (Bol et al, 1996).…”

Induced systemic resistance in wounded rice plants

“…In several plants, members of PR-protein families one to nine are known to be wound-induced (see, e.g. Bol et al, 1996;Lawton and Lamb, 1987;Parsons et al, 1989;Pautot et al, 1993;Weiss and Bevan, 1991; see also Figure 5) and several of these have antifungal activity (Liu et al, 1994;Lorito et al, 1994;Ponstein et al, 1994;Sela-Buurlage et al, 1993), supporting the notion of crossresistance against opportunistic wound pathogens. The results presented here extend the picture of the wound response to enhanced resistance against a highly virulent pathogen attacking intact tissue located remotely from the site of wounding.…”

“…Since jasmonates are derived from polyunsaturated C18 fatty acids, the corresponding signalling pathway has been referred to as the octadecanoid pathway (reviewed by Sembdner and Parthier, 1993). In the SAR model plant, tobacco, wounding and pathogen attack induce different members of multigene-families PR1 to PR5 (reviewed by Bol et al, 1996), suggesting that the wound and pathogen response pathways are distinct. Both pathways may not only be distinct but even exclusive, based on the observation of inhibition of wound-or JA-induced accumulation of proteinase inhibitors in tomato by SA or acetyl-SA (Doares et al, 1995;Pena-Cortes et al, 1993).…”

Salicylic acid-independent plant defence pathways

“…However, several lines of evidence indicate that their respective response pathways are distinct, or even antagonistic. For instance, in tobacco, wounding and pathogen attack show differential activation of different members of the PR gene families 33 . Wounding appears to activate basic PR genes, whereas pathogen attack predominantly leads to acidic PR gene expression.…”