Processing extracellular information: MLO signaling in plant reproduction

Plant cells must communicate with their external environment in order to mount appropriate responses. MLO (Mildew Resistance Locus-O) calcium channels play a key role in a variety of plant cell responses during growth and development as well as in responses to pathogens. MLO channels act downstream of FERONIA-type receptor-like kinases and form part of a conserved signaling module that optimizes cellular responses to extracellular information. The mechanisms through which RLK signaling activate MLO channel activity are currently being investigated and include selective trafficking in response to ligand-mediated signaling and phosphorylation by cytoplasmic kinases in the RLK signal transduction cascade. Several MLO genes are expressed in the reproductive tract and mediate interactions between pollen and the maternal tissues of the reproductive tract on the way to the female gametophyte. For example, NORTIA (NTA, MLO7) undergoes signal-mediated polar trafficking in the synergids in order to accumulate at the filiform apparatus and promote pollen tube bursting so that the sperm cells are delivered to the female gametophyte. New findings on the regulation of MLO protein trafficking and MLO participation in other stages of reproduction will be presented.