Pathogen defence in plants - a paradigm of biological complexity

The functional, spatial and temporal complexity of pathogen defence in plants is becoming ever-more apparent, Functional complexity begins with the exogenous signals perceived from the pathogen, continues with the mechanisms of signal perception and signal transduction, and results in extensive 'reprogramming' of cellular metabolism, involving large changes in gene activity. The spatial organization of these reactions is similarly complex and affects intracellular compartmentation, the fate of cells and, ultimately, the tissues that surround the infection site. The highly dynamic nature of the response adds temporal complexity. Thus, pathogen defence entails a major shift in metabolic activity, rather than altered expression of a few unique, defence-related genes, The observed complexity serves as a paradigm of the flexibility and plasticity of plant metabolism.