Exciting prospects for plants with greater disease resistance

Abstract

The spread of plant pathogens and insect pests is increasing worldwide. Several strategies have been used to increase crop resistance toward these pathogens, including expression of gene products that are toxic to pathogens or enhance the plants own natural resistance mechanisms. Such introduced genes are commonly placed under the control of promoters that lead to the production of these substances in all tissues of the plant. However, this can have detrimental effects on plant growth and crop yield. To reduce unwanted expression in uninfected tissues and to increase the chance of success of increasing disease resistance, we constructed synthetic promoters containing defined cis-acting elements, and showed that seven different elements direct high-level local expression around infection sites (Fig. 1Fig. 1) [1xSynthetic plant promoters containing defined regulatory elements provide novel insights into pathogen- and wound-induced signalling. Rushton, P.J. et al. Plant Cell. 2002; 14: 749–762Crossref | PubMed | Scopus (232)See all References[1]. The elements can be divided into three groups; W boxes, GCC-like boxes and Box D. Some also direct wound-inducible expression (Fig. 2Fig. 2).Fig. 1Transgenic Arabidopsis plants containing the synthetic promoter 4×W1::GUS two days after infection with Peronospora parasitica. Blue spots show the activity of the synthetic promoter at attempted infection sites. Scale bar = 2mm. Reproduced, with permission, from Ref. [1xSynthetic plant promoters containing defined regulatory elements provide novel insights into pathogen- and wound-induced signalling. Rushton, P.J. et al. Plant Cell. 2002; 14: 749–762Crossref | PubMed | Scopus (232)See all References[1].View Large Image | Download PowerPoint SlideFig. 2A transgenic Arabidopsis leaf containing 4×S::GUS that has been cut. Wound-induced expression is seen in a ‘wave’ around the cut sites. Scale bar = 5mm.View Large Image | Download PowerPoint SlideAn important discovery was that certain elements differ in their responses to pathogens. Some respond to all tested pathogens whereas others directed expression with only some of them. Crucially, the synthetic promoters are also active during compatible interactions. It is under such circumstances that drastic crop yield losses occur and in these situations biotechnology might be of great benefit. Currently, we are using these promoters to produce crop plants with increased disease resistance. We also showed that the synthetic promoters are not only active in the plant from which they originated but also in other species. This suggests that the synthetic promoters would be of general use and shows that signalling in plant defence is largely conserved across species boundaries.Our work also provides new insights into signalling during the plant defence response. It shows that the responses to wounding and pathogens can operate through the same DNA element and that similar elements, differing in only one base pair, can have drastically different expression patterns.