Department of Biology, San Francisco State University, San Francisco, CA 94132, USA.
Mol Microbiol. 2012 Jun;84(5):892-920. doi: 10.1111/j.1365-2958.2012.08064.x. Epub 2012 May 4.
Although diminutive in size, bacteria possess highly diverse and spatially confined cellular structures. Two related alphaproteobacteria, Sinorhizobium meliloti and Caulobacter crescentus, serve as models for investigating the genetic basis of morphological variations. S. meliloti, a symbiont of leguminous plants, synthesizes multiple flagella and no prosthecae, whereas C. crescentus, a freshwater bacterium, has a single polar flagellum and stalk. The podJ gene, originally identified in C. crescentus for its role in polar organelle development, is split into two adjacent open reading frames, podJ1 and podJ2, in S. meliloti. Deletion of podJ1 interferes with flagellar motility, exopolysaccharide production, cell envelope integrity, cell division and normal morphology, but not symbiosis. As in C. crescentus, the S. meliloti PodJ1 protein appears to act as a polarity beacon and localizes to the newer cell pole. Microarray analysis indicates that podJ1 affects the expression of at least 129 genes, the majority of which correspond to observed mutant phenotypes. Together, phenotypic characterization, microarray analysis and suppressor identification suggest that PodJ1 controls a core set of conserved elements, including flagellar and pili genes, the signalling proteins PleC and DivK, and the transcriptional activator TacA, while alternative downstream targets have evolved to suit the distinct lifestyles of individual species.
尽管细菌体积微小，但它们拥有高度多样化和空间受限的细胞结构。两种相关的α-变形菌，根瘤菌和新月柄杆菌，被用作研究形态变异遗传基础的模型。根瘤菌是豆科植物的共生菌，合成多个鞭毛而没有菌毛，而新月柄杆菌是一种淡水细菌，只有一个极生鞭毛和柄。PodJ 基因最初在新月柄杆菌中被鉴定为参与极性细胞器发育的基因，在根瘤菌中被分为两个相邻的开放阅读框，PodJ1 和 PodJ2。PodJ1 的缺失会干扰鞭毛运动、胞外多糖的产生、细胞包膜的完整性、细胞分裂和正常形态，但不影响共生。与新月柄杆菌一样，根瘤菌 PodJ1 蛋白似乎充当极性信标，并定位于较新的细胞极。微阵列分析表明，podJ1 影响至少 129 个基因的表达，其中大多数与观察到的突变表型相对应。综合表型特征、微阵列分析和抑制子鉴定表明，PodJ1 控制着一组核心保守元件，包括鞭毛和菌毛基因、信号蛋白 PleC 和 DivK 以及转录激活因子 TacA，而替代的下游靶标已经进化以适应特定物种的独特生活方式。
