Antonaru Laura A, Nürnberg Dennis J
Department of Life Sciences, Imperial College, London SW7 2AZ, UK.
FEMS Microbiol Lett. 2017 Aug 15;364(15). doi: 10.1093/femsle/fnx154.
Cell differentiation is one of the marks of multicellular organisms. Terminally specialised nitrogen-fixing cells, termed heterocysts, evolved in filamentous cyanobacteria more than 2 Gya. The development of their spacing pattern has been thoroughly investigated in model organisms such as Anabaena sp. PCC 7120. This paper focuses on the more complex, branching cyanobacterium Mastigocladus laminosus (Stigonematales). Contrary to what has been previously published, a heterocyst spacing pattern is present in M. laminosus but it varies with the age of the culture and the morphology of the cells. Heterocysts in young, narrow trichomes were more widely spaced (∼14.8 cells) than those in old, wide trichomes (∼9.4 cells). Biochemical and transgenic experiments reveal that the heterocyst spacing pattern is affected by the heterocyst inhibitor PatS. Addition of the pentapeptide RGSGR (PatS-5) to the growth medium and overexpression of patS from Anabaena sp. PCC 7120 in M. laminosus resulted in the loss of heterocyst differentiation under nitrogen deprivation. Bioinformatics investigations indicated that putative PatS sequences within cyanobacteria are highly diverse, and fall into two main clades. Both are present in most branching cyanobacteria. Despite its more complex, branching phenotype, M. laminosus appears to use a PatS-based pathway for heterocyst differentiation, a property shared by Anabaena/Nostoc.
细胞分化是多细胞生物的标志之一。终末特化的固氮细胞，即异形胞，在超过20亿年前在丝状蓝细菌中进化而来。它们的间距模式的发育已经在诸如鱼腥藻属PCC 7120等模式生物中得到了深入研究。本文聚焦于更为复杂的分支蓝细菌层理鞭枝藻（颤藻目）。与之前发表的内容相反，层理鞭枝藻中存在异形胞间距模式，但它会随着培养物的年龄和细胞形态而变化。年轻、狭窄藻丝中的异形胞比年老、宽阔藻丝中的异形胞间距更宽（约14.8个细胞对约9.4个细胞）。生化和转基因实验表明，异形胞间距模式受异形胞抑制剂PatS影响。向生长培养基中添加五肽RGSGR（PatS-5）以及在层理鞭枝藻中过表达来自鱼腥藻属PCC 7120的patS，导致在氮剥夺条件下异形胞分化丧失。生物信息学研究表明，蓝细菌中的假定PatS序列高度多样，可分为两个主要分支。两者在大多数分支蓝细菌中都存在。尽管层理鞭枝藻具有更复杂的分支表型，但它似乎使用基于PatS的途径进行异形胞分化，这是鱼腥藻属/念珠藻属共有的特性。
