**1. Introduction**

Fluctuations in the prevailing environmental conditions, including light availability and intensity, CO2/O2 ratio, temperature, and nutrient or water supply, require rapid metabolic switches to maintain proper metabolism. To achieve this, a multitude of regulatory mechanisms are needed to communicate between the various metabolic branches to adjust fluxes through all routes related to central carbon and nitrogen metabolism. Despite considerable effort in understanding the genetics and biochemistry of plant primary metabolism, insights into the underlying mechanisms governing such acclimations and the involved regulatory circuits are still fragmentary. A better knowledge on those aspects would certainly help to engineer crop plants to maintain high yields under fluctuating environmental conditions.

Over the past decades, tremendous progress has been made to unravel the extraordinary complexity of plant primary metabolism from a biochemical and genetic point of view. Special attention has been paid to carbon and nitrogen assimilation and their subsequent metabolism [1–3]. Biochemical reactions of canonical pathways, such as the Calvin–Benson cycle, the oxidative pentose phosphate pathway, glycolysis, the tricarboxylic acid (TCA) cycle, and photorespiration have been thoroughly investigated [4–8]. However, given that many of those pathways run simultaneously, there are gaps regarding how these pathways are coordinated with each other, intertwined, and regulated. In this special issue, we invited authors to contribute to new studies encompassing the field of regulation of pathways that drive plant primary metabolism in oxygenic phototrophs, particularly focusing on photorespiration, photosynthesis, and glycolysis, as well as metabolite regulation, signaling and transport. In addition, natural acclimation strategies to a changing environment are included.
