Figure 1.

Graphical representation of main targets of key regulatory protein PII under nitrogen-replete cells of Nostoc. Light-blue arrows represent interactions between protein PII and its main protein partners [28]. Red arrows indicate upregulation (↑) of the rbcL protein, upregulation of the gene hetR expression and influence on cellular processes that were identified in this study and in our previous work [22]. Green arrows indicate NtcA regulation, and black arrows show involvement of hetR and rbcL in heterocyst differentiation and CO₂ fixation, respectively.