The orphan response regulator DigR is required for synthesis of extracellular matrix fibrils in Myxococcus xanthus. Myxococcus xanthus

In Myxococcus xanthus, two component systems have crucial roles in regulating motility behavior and development. Here, we describe an orphan response regulator consisting of an N-terminal receiver domain and a C-terminal DNA binding domain, which is required for A- and type IV pili dependent gliding motility. Genetic evidence suggests that phosphorylation of the conserved, phosphorylatable aspartate residue in the receiver domain is required for DigR activity. Consistent with the defect in type IV pili dependent motility, a digR mutant is slightly reduced in type IV pili biosynthesis and the composition of the extracellular matrix fibrils is abnormal with an increased content of polysaccharides and decreased accumulation of the FibA metalloprotease. Using genome-wide transcriptional profiling, 118 genes were identified that are directly or indirectly regulated by DigR. These genes only include two genes, agmQ and cheY4, previously implicated in A- and type IV pili dependent motility, respectively. In silico analyses showed that 36% of the differentially expressed genes are likely to encode exported proteins. Moreover, four genes encoding homologs of ECF sigma factors, which typically control aspects of cell envelope homeostasis, are differentially expressed in a digR mutant. We suggest that the DigR response regulator has an important function in cell envelope homeostasis and that the motility defects in a digR mutant are instigated by the abnormal cell envelope and abnormal expression of agmQ and cheY4. Keywords: vegetative analysis (delta)DigR / DK1622 (wt) Overall design: 5 biological replicates each; normalized ratios to vegetative cells of DK1622 (wt)

在黄色粘球菌（Myxococcus xanthus）中，双组分系统（two component systems）在调控运动行为与发育过程中发挥关键作用。本研究报道一种包含N端接收结构域与C端DNA结合结构域的孤儿应答调控蛋白（orphan response regulator），其对于A型依赖运动以及IV型菌毛（type IV pili）依赖的滑行运动不可或缺。遗传学证据表明，接收结构域中保守的可磷酸化天冬氨酸残基的磷酸化修饰对于DigR的活性至关重要。
与IV型菌毛依赖的运动缺陷表型一致，digR突变体的IV型菌毛生物合成量略有降低，且其细胞外基质纤维的组成异常：多糖含量升高，而FibA金属蛋白酶的积累量下降。通过全基因组转录谱分析（genome-wide transcriptional profiling），我们鉴定出118个受DigR直接或间接调控的基因。这些基因中仅包含两个此前分别被报道与A型依赖运动、IV型菌毛依赖运动相关的基因：agmQ与cheY4。
生物信息学分析（in silico）显示，在差异表达基因中，有36%的基因可能编码分泌型蛋白。此外，在digR突变体中，四个编码ECFσ因子（ECF sigma factors）同源物的基因存在差异表达，这类因子通常参与调控细胞包膜稳态相关过程。
我们推测，DigR应答调控蛋白在细胞包膜稳态维持中发挥重要功能，而digR突变体的运动缺陷正是由异常的细胞包膜状态以及agmQ与cheY4的异常表达所引发的。
关键词：营养生长状态分析 ΔDigR / DK1622（野生型，wt）
实验设计：每组设置5个生物学重复；数据为以DK1622野生型营养生长细胞为参照的标准化比值。