Regulation of development in Myxococcus xanthus by the second messenger c-di-GMP

黄粘球菌的细胞在营养匮乏的情况下启动发育程序，最终形成充满孢子的子实体。这一发育计划的完成关键取决于基因表达、运动及其调节、细胞间信号以及基于核苷酸的第二信使信号的临时调节变化的密切协调。这些第二信使包括由RelA合成的(p)ppGpp，以及我们最近展示的c-di-GMP。与营养生长的细胞相比，饥饿期间c-二gmp的积累水平升高，这种增加对完成发育至关重要，而过量的c-二gmp不会干扰发育。酶活性二胍酸环化酶DmxB对发育至关重要，并负责c-二gmp水平的增加。此外，我们已经证明DmxB仅在发育过程中合成，并通过诱导参与外多糖合成的基因的转录来刺激外多糖的积累。我们的数据支持DmxB在多个水平上受到调节的假设，包括转录、变构和其n端受体结构域的磷酸化。由于DmxB在功能上可以部分被异源二胍酸环化酶取代，这些数据表明，c-二gmp的最低阈值水平对于成功完成这一多细胞发育程序至关重要。我们还发现酶活性磷酸二酯酶PmxA对发育至关重要，然而，缺乏PmxA不会导致c-di-GMP的整体细胞水平变化。本项目的最终目标是了解黄原草在发育过程中如何调节c-di-GMP的积累，并确定结合c-di-GMP的效应蛋白，并实现改变c-di-GMP水平的影响。为此，我们会在“优先计划”的首3年资助期内，集中进行三项综合研究。首先，我们的目标是确定调节发育特异性二胍酸环化酶DmxB的感觉输入。其次，我们的目标是鉴定在发育过程中活跃的c-二gmp结合效应蛋白。第三，我们的目标是确定发育特异性磷酸二酯酶PmxA的机制。

Cells of Myxococcus xanthus initiates developmental programme in response to nutrient starvation that culminates in the formation of spore-filled fruiting bodies. Completion of this developmental programme crucially depends on the close coordination of temporally regulated changes in gene expression, motility and its regulation, intercellular signaling, as well as signaling by nucleotide-based second messengers. These second messengers include (p)ppGpp synthesized by RelA and, as we have recently shown, c-di-GMP. c-di-GMP accumulates at elevated levels during starvation in comparison to vegetatively growing cells and this increase is essential for completion of development whereas excess c-di-GMP does not interfere with development. The enzymatically active diguanylate cyclase DmxB is essential for development and responsible for this increase in the c-di-GMP level. Also, we have demonstrated that DmxB is only synthesized during development and functions to stimulate exopolysaccharide accumulation by inducing transcription of genes involved in exopolysaccharide synthesis. Our data support the hypothesis that DmxB is regulated at multiple levels including transcription, allosterically and by phosphorylation of its N-terminal receiver domain. Because DmxB can partially be functionally replaced by a heterologous diguanylate cyclase these data suggest that a minimum threshold level of c-di-GMP is essential for successful completion of this multicellular developmental program. We have also identified the enzymatically active phosphodiesterase PmxA as essential for development, however, lack of PmxA does not cause a change in the global cellular level of c-di-GMP. The ultimate goals of this project are to understand how c-di-GMP accumulation is regulated during development in M. xanthus and to identify the effector proteins that bind c-di-GMP and implement the effects of changing c-di-GMP levels. To this end, we will focus on three lines of integrated research in the first 3-year funding period of this Priority Programme. Firstly, we aim to identify the sensory input(s) that regulates the development-specific diguanylate cyclase DmxB. Secondly, we aim to identify c-di-GMP binding effector proteins that are active during development. Thirdly, we aim to determine the mechanism of the development-specific phosphodiesterase PmxA.