Khudyakov Ivan, Gladkov Grigory, Elhai Jeff
All-Russia Research Institute for Agricultural Microbiology, 196608 Saint-Petersburg, Russia.
Department of Biology, Virginia Commonwealth University, Richmond, VA 23284, USA.
Life (Basel). 2020 Dec 4;10(12):326. doi: 10.3390/life10120326.
The filamentous cyanobacterium sp. PCC 7120 produces, during the differentiation of heterocysts, a short peptide PatS and a protein HetN, both containing an RGSGR pentapeptide essential for activity. Both act on the master regulator HetR to guide heterocyst pattern formation by controlling the binding of HetR to DNA and its turnover. A third small protein, PatX, with an RG(S/T)GR motif is present in all HetR-containing cyanobacteria. In a nitrogen-depleted medium, inactivation of does not produce a discernible change in phenotype, but its overexpression blocks heterocyst formation. Mutational analysis revealed that PatX is not required for normal intercellular signaling, but it nonetheless is required when PatS is absent to prevent rapid ectopic differentiation. Deprivation of all three negative regulators-PatS, PatX, and HetN-resulted in synchronous differentiation. However, in a nitrogen-containing medium, such deprivation leads to extensive fragmentation, cell lysis, and aberrant differentiation, while either PatX or PatS as the sole HetR regulator can establish and maintain a semiregular heterocyst pattern. These results suggest that tight control over HetR by PatS and PatX is needed to sustain vegetative growth and regulated development. The mutational analysis has been interpreted in light of the opposing roles of negative regulators of HetR and the positive regulator HetL.
丝状蓝细菌集胞藻PCC 7120在异形胞分化过程中产生一种短肽PatS和一种蛋白质HetN，两者都含有对活性至关重要的RGSGR五肽。它们都作用于主调控因子HetR，通过控制HetR与DNA的结合及其周转来引导异形胞模式形成。第三种小蛋白质PatX，具有RG(S/T)GR基序，存在于所有含HetR的蓝细菌中。在缺氮培养基中，PatX的失活不会导致表型出现明显变化，但其过表达会阻止异形胞形成。突变分析表明，正常的细胞间信号传导不需要PatX，但在没有PatS时，它对于防止快速异位分化是必需的。去除所有三种负调控因子——PatS、PatX和HetN——会导致同步分化。然而，在含氮培养基中，这种去除会导致广泛的碎片化、细胞裂解和异常分化，而单独的PatX或PatS作为唯一的HetR调控因子可以建立并维持半规则的异形胞模式。这些结果表明，需要通过PatS和PatX对HetR进行严格控制，以维持营养生长和调控发育。根据HetR的负调控因子和正调控因子HetL的相反作用对突变分析进行了解释。
