THE ENGINEERING OF PLANT DISEASE RESISTANCE BASED ON AN UNDERSTANDING OF DISEASE RESISTANCE SIGNALING PATHWAYS
C ROMMENS, B ZHANG, C TAYLOR and KATHY SWORDS
Monsanto Company, 700 Chesterfield Parkway, St. Louis, MO 63198, USA
Extensive analyses of plant responses to pathogen infection in many different laboratories have shown that plants contain highly complex resistance pathways comprising hundreds of different proteins. Based on a partial understanding of these responses, several different strategies are currenly being employed by Monsanto and others to engineer broad-spectrum disease control in transgenic plants. One strategy is centered around single resistance (R-) genes. Activated R-genes trigger signaling pathways leading to both a localized hypersensitivity (HR) and a systemic induction of pathogenesis-related (PR) proteins. Since R-gene products contain conserved domains, they can be cloned by homology for transfer to crops of interest. Another strategy is based on the finding that different classes of downstream pathogen-inducible genes display in vitro anti-microbial or anti-insect activity. Members of these classes encode, apart from PR proteins, defensins, thionins, lipid transfer proteins, and proteinase inhibitors. Overexpression of pathogen-inducible genes has in some cases been shown to enhance disease resistance levels. The recent isolation of genes encoding putative transcription factors in disease control allowed development of a third strategy to engineer resistance. This strategy is aimed at enhancing levels of disease control by overexpressing genes such as the Arabidopsis Npr1 gene. Many additional signaling proteins may play key roles in and should be tested for their efficacy. To include "all" plant proteins in searches for novel resistance determinants, strategies are developed that utilize genomics-based technologies such as microarraying and high-throughput EST sequencing.