CSIRO PUBLISHING www.publish.csiro.au/journals/fpb Functional Plant Biology, 2005, 32, 21–34 Review: Plant defence responses: conservation between models and crops Jonathan P. Anderson A , Louise F. Thatcher A,B and Karam B. Singh A,C A CSIRO Plant Industry, Centre for environment and life sciences, Private bag 5, Wembley, WA 6913, Australia. B Soil Science and Plant Nutrition, School of Earth and Geographical Sciences, The University of Western Australia, Crawley, WA 6009, Australia. C Corresponding author. Email: Karam.Singh@csiro.au Abstract. Diseases of plants are a major problem for agriculture world wide. Understanding the mechanisms employed by plants to defend themselves against pathogens may lead to novel strategies to enhance disease resistance in crop plants. Much of the research in this area has been conducted with Arabidopsis as a model system, and this review focuses on how relevant the knowledge generated from this model system will be for increasing resistance in crop plants. In addition, the progress made using other model plant species is discussed. While there appears to be substantial similarity between the defence responses of Arabidopsis and other plants, there are also areas where significant differences are evident. For this reason it is also necessary to increase our understanding of the specific aspects of the defence response that cannot be studied using Arabidopsis as a model. Keywords: ethylene, jasmonate, pathogen, pathogenesis related genes, plant defense signalling pathways, plant disease, salicylic acid. Introduction Pathogens and insect pests cause widespread losses to agriculture throughout the world on an annual basis. In developed countries, losses are typically around 20% of the potential yeild, while in developing countries losses are normally significantly greater (Bent and Yu 1999). In light of these substantial losses there has been considerable research directed at understanding how plants defend themselves against a range of biotic stresses. Somewhat paradoxically, given the large annual losses faced by modern monoculture agriculture, the actual occurrence of disease on the scale of an individual plant is relatively infrequent, even though plants are commonly in contact with numerous potential pathogens. The low frequency of disease is evidence of the existence of effective plant defence systems. The plant defence process consists of both preformed and induced defences that can either prevent the pathogen from entering the plant or obtaining nutrient for growth and reproduction (see Thatcher et al. 2004 for review). The defence response can also be divided into non-host resistance, where a plant is resistant to all races of a pathogen, and host resistance, where a plant is resistant to some but not all races of a pathogen (Heath 2000). However, the two types Abbreviations used: CHORD, cystine- and histidine-rich domains; ERF, ethylene response factor; ET, ethylene; JA, jasmonic acid; MJ, methyl jasmonate; SA, salicylic acid; SAR, systemic acquired resistance. of resistance have substantial overlap, with plants responding in similar ways in host and non-host interactions and several components of the signalling pathways common to both types of resistance (Thordal-Christensen 2003). The defining difference between non-host and host interactions is the ability of the potential pathogen to overcome a series of obstacles to successfully infect a host plant. The plant cytoskeleton is often considered to be one of the first obstacles encountered by the pathogen (Thordal-Christensen 2003). An example of the importance of the cytoskeleton was shown by the disruption of the actin cytoskeleton of barley, wheat, cucumber and tobacco that resulted in cellular penetration by several non-host fungi (Kobayashi et al. 1997). However, whether the cytoskeleton itself is an obstacle to pathogen ingress or simply a requirement for the expression of other resistance responses is unclear. The preformed defences also include chemical barriers such as the saponin avenacin of oats where mutant lines with reduced production of avenacin were more susceptible to the non-host pathogens Gaeumannomyces graminis var. tritici and Fusarium culmorum (Papadopoulou et al. 1999). Other methods employed by the plant to produce a non-host interaction include the perception of non-specific © CSIRO 2005 10.1071/FP04136 1445-4408/05/010021