Mitogen-activated protein kinase (MAPK) cascades are evolutionarily conserved signalling modules with essential regulatory functions in plants

Signal transduction networks are essential to plant growth and development, allowing cells and tissues to perceive and respond to continuous changes in their environment. Multiple signalling pathways exist in plant cells, controlling important processes including hormone and light perception, pathogen defence, stress survival, cell division and circadian rhythms. Until 10 years ago, the plant signal transduction pathways that transmit well-known stimuli were viewed as black boxes. Through advances in Arabidopsis genetics and numerous other important approaches, individual elements and short signalling segments and complexes have been discovered, resulting in a greying of the black boxes. Furthermore, the molecular mechanisms by which signalling pathways crosstalk with each other or by which specificity is conferred within a complex signalling network are currently areas of intensive research in plant biology and eukaryotic biology in general. It has long been recognised that most aspects of plant growth and physiology are regulated by networks of signalling mechanisms rather than by linear signal transduction pathways, rendering plants particularly attractive for dissecting crosstalk and specificity mechanisms. In this issue of Current Opinion in Plant Biology, recent advances in rapidly moving areas of plant signalling research are reviewed and important newly arising open questions are formulated.