Abstract
In unicellular bacteria, the ParA and ParB proteins segregate chromosomes and coordinate this process with cell division and chromosome replication. During sporulation of mycelial Streptomyces, ParA and ParB uniformly distribute multiple chromosomes along the filamentous sporogenic hyphal compartment, which then differentiates into a chain of unigenomic spores. However, chromosome segregation must be coordinated with cell elongation and multiple divisions. Here, we addressed the question of whether ParA and ParB are involved in the synchronization of cell-cycle processes during sporulation in Streptomyces. To answer this question, we used time-lapse microscopy, which allows the monitoring of growth and division of single sporogenic hyphae. We showed that sporogenic hyphae stop extending at the time of ParA accumulation and Z-ring formation. We demonstrated that both ParA and ParB affect the rate of hyphal extension. Additionally, we showed that ParA promotes the formation of massive nucleoprotein complexes by ParB. We also showed that FtsZ ring assembly is affected by the ParB protein and/or unsegregated DNA. Our results indicate the existence of a checkpoint between the extension and septation of sporogenic hyphae that involves the ParA and ParB proteins.
Highlights
Robust cell proliferation requires precise coordination of key cell-cycle processes
The explanation for these differences is that ParAB proteins are involved in the coordination of chromosome segregation with different cell-cycle processes, such as chromosome replication, cell growth and/ or cell division (C. crescentus, Mycobacterium smegmatis and Streptomyces coelicolor)
Previous reports have indicated that the extension of the sporogenic hyphae stops before the commencement of further stages of development, that is, chromosome condensation, segregation and hyphae septation [50]
Summary
Robust cell proliferation requires precise coordination of key cell-cycle processes. Active chromosome segregation begins soon after the initiation of replication in the oriC region (origin of replication). ParAB deletion is associated with diverse phenotypes in different bacterial species; in C. crescentus the genes are essential, but in B. subtilis their deletion has only a minor effect on the growth. The explanation for these differences is that ParAB proteins are involved in the coordination of chromosome segregation with different cell-cycle processes, such as chromosome replication (in B. subtilis and Vibrio cholerae), cell growth and/ or cell division (C. crescentus, Mycobacterium smegmatis and Streptomyces coelicolor)
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