Nitrogen storage regulation by PII protein: lessons learned from taxonomic outliers.

The paper 'Interaction of N‐acetyl‐l‐glutamate kinase with the PII signal transducer in the non‐photosynthetic alga Polytomella parva: Co‐evolution towards a hetero‐oligomeric enzyme' by Selim et al. highlights how the study of a true taxonomic oddity, the heterotrophic unicellular alga P. parva, has been instrumental in uncovering the large potential for adaptive variation in the signaling complex of PII with the enzyme N‐acetylglutamate kinase (NAGK). This complex modifies the regulatory properties of NAGK, allowing nitrogen stockpiling as arginine. In P. parva, a stable PII‐NAGK complex is formed which lacks regulation by canonical PII effectors but which exhibits novel adaptive responses to nitrogen abundance mediated by glutamine, a neo‐effector of PII proteins of photosynthetic eukaryotes. [ABSTRACT FROM AUTHOR]