A Putative O-Linked β-N-Acetylglucosamine Transferase Is Essential for Hormogonium Development and Motility in the Filamentous Cyanobacterium Nostoc punctiforme
A Putative O-Linked β-N-Acetylglucosamine Transferase Is Essential for Hormogonium Development and Motility in the Filamentous Cyanobacterium Nostoc punctiforme
复制标题
DOI：
10.1128/jb.00075-17
复制
发表时间：
2017-05-01
影响因子：
3.2
通讯作者：
Risser, Douglas D.
中科院分区：
文献类型：
--
作者：
Khayatan, Behzad;Bains, Divleen K.;Risser, Douglas D.
大多数种类的丝状蓝藻能够滑行运动，可能通过一个保守的IV型菌毛样系统，也可能分泌motilityassociated多糖。在这些生物体的一个子集中，只有在藻殖体短暂分化后才能实现运动性，藻殖体是进入非生长状态的专用于运动性的特化细丝。尽管藻殖体对许多丝状蓝藻的生命周期至关重要，但藻殖体发育的分子调控在很大程度上是不确定的。为了系统地鉴定杂囊形成丝状蓝藻模式点状念珠藻中藻殖体发育和运动所必需的基因，采用正向遗传筛选。使用该筛选鉴定的第一个基因，命名为ogtA，编码推定的O-连接的β-N-乙酰葡糖胺转移酶（OGT）。ogtA的缺失废除运动，而异位表达的ogtA诱导hormogonium发展，即使在hormogonium抑制条件下。ogtA的转录在殖子诱导后迅速上调（1小时），并且OgtA-GFPuv融合蛋白定位于细胞质。在发育中的藻殖期，PilA而不是HmpD的积累依赖于ogtA。逆转录定量PCR（RT-qPCR）分析表明野生型和Δ ogtA突变株中pilA转录物的水平相等，而由pilA 5'方向的基因间区域与gfp融合组成的报道构建体在Δ ogtA突变株中产生的荧光水平低于野生型。与野生型相比，Delta ogtA突变菌株中的藻藻多糖的产生减少，但与pilA缺失菌株中的藻多糖的产生相当。总的来说，这些结果意味着O-GlcNAc蛋白修饰调节PilA的积累，通过转录后机制在发展hormogonia.IMPORTANCE丝状蓝藻是最发育复杂的原核生物。诸如Nostoc punctiforme的物种发展出一系列的细胞类型，包括固氮异形胞、孢子样无动细胞和能动的藻殖体，这些细胞在传播以及与植物和真菌建立固氮共生关系中发挥作用。这些共生体是全球固氮的主要贡献者。尽管藻殖体对丝状蓝藻的生命周期和共生体的建立至关重要，但藻殖体发育的分子调控在很大程度上是不确定的。我们采用了遗传筛选，以确定所必需的基因的藻发育和运动的念珠藻。使用该筛选鉴定的第一个基因编码真核样O-连接的β-N-乙酰葡糖胺转移酶，其为PilA在藻殖体中积累所需。
Most species of filamentous cyanobacteria are capable of gliding motility, likely via a conserved type IV pilus-like system that may also secrete a motilityassociated polysaccharide. In a subset of these organisms, motility is achieved only after the transient differentiation of hormogonia, which are specialized filaments that enter a nongrowth state dedicated to motility. Despite the fundamental importance of hormogonia to the life cycles of many filamentous cyanobacteria, the molecular regulation of hormogonium development is largely undefined. To systematically identify genes essential for hormogonium development and motility in the model heterocyst-forming filamentous cyanobacterium Nostoc punctiforme, a forward genetic screen was employed. The first gene identified using this screen, designated ogtA, encodes a putative O-linked beta-N-acetylglucosamine transferase (OGT). The deletion of ogtA abolished motility, while ectopic expression of ogtA induced hormogonium development even under hormogonium-repressing conditions. Transcription of ogtA is rapidly upregulated (1 h) following hormogonium induction, and an OgtA-GFPuv fusion protein localized to the cytoplasm. In developing hormogonia, accumulation of PilA but not HmpD is dependent on ogtA. Reverse transcriptionquantitative PCR (RT-qPCR) analysis indicated equivalent levels of pilA transcript in the wild-type and.ogtA mutant strains, while a reporter construct consisting of the intergenic region in the 5' direction of pilA fused to gfp produced lower levels of fluorescence in the Delta ogtA mutant strain than in the wild type. The production of hormogonium polysaccharide in the Delta ogtA mutant strain is reduced compared to that in the wild type but comparable to that in a pilA deletion strain. Collectively, these results imply that O-GlcNAc protein modification regulates the accumulation of PilA via a posttranscriptional mechanism in developing hormogonia.IMPORTANCE Filamentous cyanobacteria are among the most developmentally complex prokaryotes. Species such as Nostoc punctiforme develop an array of cell types, including nitrogen-fixing heterocysts, spore-like akinetes, and motile hormogonia, that function in dispersal as well as the establishment of nitrogen-fixing symbioses with plants and fungi. These symbioses are major contributors to global nitrogen fixation. Despite the fundamental importance of hormogonia to the life cycle of filamentous cyanobacteria and the establishment of symbioses, the molecular regulation of hormogonium development is largely undefined. We employed a genetic screen to identify genes essential for hormogonium development and motility in Nostoc punctiforme. The first gene identified using this screen encodes a eukaryotic-like O-linked beta-N-acetylglucosamine transferase that is required for accumulation of PilA in hormogonia.