Instituto de Bioquímica Vegetal y Fotosíntesis, Consejo Superior de Investigaciones Científicas and Universidad de Sevilla, E-41092, Sevilla, Spain.
Genetics and Experimental Bioinformatics, Faculty of Biology, University of Freiburg, D-79104, Freiburg, Germany.
Environ Microbiol. 2019 Jul;21(7):2544-2558. doi: 10.1111/1462-2920.14647. Epub 2019 May 20.
Nitrogen is frequently limiting microbial growth in the environment. As a response, many filamentous cyanobacteria differentiate heterocysts, cells devoted to N fixation. Heterocyst differentiation is under the control of the master regulator HetR. Through the characterization of the HetR-dependent transcriptome in Nostoc sp. PCC 7120, we identified the new candidate genes likely involved in heterocyst differentiation. According to their maximum induction, we defined E-DIF (early in differentiation) and L-DIF (late in differentiation) genes. Most of the genes known to be involved in the critical aspects of heterocyst differentiation or function were also classified into these groups, showing the validity of the approach. Using fusions to gfp, we verified the heterocyst-specific transcription of several of the found genes, antisense transcripts and potentially trans-acting sRNAs. Through comparative sequence analysis of promoter regions, we noticed the prevalence of the previously described DIF1 motif and identified a second motif, called DIF2, in other promoters of the E-DIF cluster. Both motifs are widely conserved in heterocystous cyanobacteria. We assigned alr2522 as a third member, besides nifB and nifP, to the CnfR regulon. The elements identified here are of interest for understanding cell differentiation, engineering of biological nitrogen fixation or production of O -sensitive molecules in cyanobacteria.
氮通常是环境中微生物生长的限制因素。作为回应，许多丝状蓝藻分化出异形胞，这些细胞专门用于固氮。异形胞的分化受主调控因子 HetR 控制。通过对 Nostoc sp. PCC 7120 中依赖 HetR 的转录组的特征分析，我们鉴定了可能参与异形胞分化的新候选基因。根据它们的最大诱导程度，我们定义了 E-DIF（分化早期）和 L-DIF（分化晚期）基因。已知参与异形胞分化或功能的关键方面的大多数基因也被归入这两个组，表明了该方法的有效性。通过与 gfp 的融合，我们验证了所发现的几个基因、反义转录物和潜在的反式作用 sRNA 的异形胞特异性转录。通过启动子区域的比较序列分析，我们注意到了先前描述的 DIF1 基序的普遍性，并在 E-DIF 簇的其他启动子中鉴定出第二个基序，称为 DIF2。这两个基序在异形胞蓝藻中广泛保守。我们将 alr2522 分配为 CnfR 调控子的第三个成员，除了 nifB 和 nifP 之外。这里鉴定的元件对于理解细胞分化、生物固氮的工程设计或在蓝藻中产生 O-敏感分子具有重要意义。
