Two component signal transduction systems that regulate the temporal and spatial expression of Myxococcus xanthus sporulation genes

ABSTRACT

When starved for nutrients, Myxococcus xanthus produces a biofilm that contains a mat of rod-shaped cells, known as peripheral rods, and aerial structures called fruiting bodies, which house thousands of dormant and stress-resistant spherical spores. Because rod-shaped cells differentiate into spherical-shaped, stress-resistant spores and spore differentiation occurs only in nascent fruiting bodies, many genes and multiple levels of regulation are required. Over the past two decades, many regulators of the temporal and spatial expression of M. xanthus sporulation genes have been uncovered. Of these sporulation gene regulators, two component signal transduction circuits, which typically contain a histidine kinase sensor protein and a transcriptional regulator known as response regulator, are among the best characterized. In this review, we discuss prototypical two component systems (Nla6S/Nla6 and Nla28S/Nla28) that regulate an early, pre-aggregation phase of sporulation gene expression during fruiting body development. We also discuss orphan response regulators (ActB and FruA) that regulate a later phase of sporulation gene expression, which begins during the aggregation stage of fruiting body development. In addition, we summarize the research on a complex two component system (Esp) that is important for the spatial regulation of sporulation.