Fig. 7: A model for NtcA-regulated FtsZ levels and cell division in Anabaena.

A Under SL (standard light) conditions, the TCA pathway in the WT operates at normal efficiency, leading to no significant changes in carbon metabolites. NtcA regulates FtsZ expression at a basal level, and cell division occurs normally without noticeable changes in cell morphology. B Under HL (high light) conditions, the efficiency of the TCA pathway slightly increased, resulting in elevated levels of succinate and citrate in the WT Anabaena strain compared to SL conditions. This metabolic shift enhances the NtcA protein level, which in turn increases FtsZ expression. The elevated FtsZ levels promote faster cell division, resulting in reduced cell length. C Under HL conditions, the TCA pathway in the gPCEM strain exhibits high efficiency, causing significantly elevated levels of fumarate, malate, citrate, and 2-OG (2-oxoglutarate, indicated by a green star). The accumulation of NtcA and 2-OG plays a major role in increasing FtsZ levels by enhancing the transcription of the ftsZ gene through the transcription factor NtcA. Consequently, the elevated FtsZ level promotes asymmetric cell division, leading to irregular cell morphology.