Possible defense molecules in barley

Abstract

The recent development of refined molecular tools to study gene structure and function, as well as the availability of genetic transformation methods for all kinds of organisms, including plants, has lent new vigor to the investigation of plant defense mechanisms, a subject with a long and distinguished tradition. A variety of approaches are being followed by molecular biologists to analyze plant responses to pathogens and pests. Three of these emerge as predominant: i) From disease to relevant molecules, a strategy that involves challenging a plant with a pathogen or pest, identifying the plant genes that are switched on in response to the challenge, and attempting to correlate the functional properties of at least some of these genes with a defense role, ii) From disease resistance to relevant molecules, an approach based on finding cosegregation of a resistance gene and certain molecular features in a near-isogenic background, iii) From molecules with toxic or deterrent properties to enhanced resistance, an approximation which implies the construction of an agronomic trait out of the known activities of appropriate molecules and their corresponding genes. It is not pertinent here to discuss the relative merits of these strategies, which are not mutually exclusive. My aim is rather to examine to what extent they have allowed the identification of possible defense molecules in barley and related species. Because of circumstantial and/or objective reasons, monocots, in general, and barley, in particular, have not been the plant systems where some of the original studies have been carried out. However, for obvious reasons a significant part of recent interest is focusing on them. Plant defense mechanisms are still far from being elucidated (see Bowles 1990), so this non-comprehensive review will have the more modest objective of summarizing some relevant information concerning possible defense molecules in barley and its close relatives.