Ustilago maydisand Maize: a Delightful Interaction

Understanding the molecular mechanisms of the interaction of Ustilago maydis with maize entails understanding the molecular mechanisms that regulate its life cycle. This chapter presents an overview of the current knowledge regarding the interaction of Ustilago maydis with maize. First, useful features that have facilitated analysis of the life cycle are described, followed by a brief synopsis of the morphological transitions that characterize the life cycle and their control by the mating-type loci and the mitogen-activated protein kinase (MAPK) and cyclic AMP (cAMP) signal transduction pathways. Lastly, specific genes known to be required or to be expressed at different stages of the infectious cycle are described. Infection of anthers at various developmental stages not only induces tumors but can also cause aberrant development of different parts of the anther. Thus, infections with U. maydis may provide important insights about floral development in maize. Hyphal fragmentation occurs within the tumors, though it has been reported that this process can occur between cells. Studies that utilized different maize lines suggested that the host can modulate the course of infection. Analysis of mutants in combination with sophisticated imaging techniques and the application of expression profiling of individual infected versus noninfected cells will allow a more precise dissection of the infectious process and identification of the genes that are differentially regulated in the partners of this "apparent" harmonious interaction.