ARMS RACE BETWEEN PHYTOPATHOGENS AND HOST PLANTS: A SIMILITUDE OF TWO NATIONS AT WAR

Abstract

Phytopathogens have coexisted with their host plants from the beginning of their existence, relying on them for shelter and nutrients to survive, therefore leading to a constant attack of host plants. On the other hand, host plants have evolved several strategies to defend themselves against pathogen attack. The attacks and counter-attacks can be likened to an “arms raceâ€, between two nations at war. Pathogens evolved strategies (arms) which include exertion of mechanical forces and secretion of biochemical substances such as enzymes and growth regulators, to attack susceptible host plants. These strategies are facilitated by the inability of the host plants to recognize certain molecules, known as PAMPs (Pathogen-Associated Molecular Patterns) from the pathogens. In a counter attack, host plants have developed receptors to recognize the presence of pathogens and PAMPs. This recognition activates PAMP-triggered immunity (PTI), thereby making the hitherto host plants resistant. Pathogens have further evolved another set of “armsâ€, known as secretion systems and effector genes, whose gene products suppress PTI, thus causing diseases. As the arms race continued, plants have evolved effector-triggered immunity (ETI) by developing intracellular resistance genes, thereby resulting to a hypersensitive reaction that follows the gene-for-gene concept. Presently, some pathogens have developed mechanisms for the suppression of ETI. In some plant-pathosystems, the plants are winning, while in others, the pathogens are winning. Phytopathological research should therefore be directed towards assisting susceptible plants to defeat phytopathogens, in order to ensure food security.