Elicitors and defence gene activation

1365-3040

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Abstract. Plants respond actively to infection and other environmental stresses by synthesizing phytoalexins and defence-related proteins. This response can be induced in plant cell suspension cultures with compounds known as elicitors. These are often carbohydrates of fungal origin. In bean, transcriptional activation of the defence genes commences less than five minutes after elicitor addition, thus it is clearly a very rapid response implying few biochemical steps exist between elicitor interaction and the initiation of defence gene transcription. The induction of phytoalexin biosynthesis during incompatible interactions of bean with Colletotrichum lindemuthianum occurs rapidly during the initial contact between the host and pathogen. This appears to be a direct response to molecular recognition of the pathogen. In compatible interactions however, the pathogen grows biotrophically and phytoalexin biosynthesis is not triggered until lesions begin to form. Thus this may be a response to tissue damage rather than direct molecular recognition. Many bean defence genes, including those regulating key points in the phytoalexin biosynthetic pathway, exist in the genome as small multigene families. In some cases there is differential regulation within a family in response to developmental and environmental signals. The analysis of the cis-acting sequences involved in the regulation of chalcone synthase has been facilitated by the use of electroporated protoplasts as a transient assay system. This work and the use of DNA footprinting and gel-retardation assays will help identify the corresponding trans-acting factors involved in the regulation of these genes. While progress is being made in understanding the mechanisms of transcriptional activation of defence genes little is known of how plants recognize pathogens and elicitors or how this signal is transduced to the nucleus.

Electronic Resource