Molecular basis and fitness implications of the interplay between light and the regulation of iron homeostasis in photosynthetic organisms

• Light impacts iron transport, demands and homeostasis in photosynthetic organisms.
• Phytochromes affect expression of Fe homeostasis genes in photosynthetic organisms.
• Light–iron interactions regulate photosynthetic potential and associated fitness.

Photosynthetic organisms respond to changes in the external environment, including responses to changes in light color, light intensity and nutrient availability. Iron is one of the nutrients that is critical for the function of photosynthetic organisms, primarily due to the high demand for iron in the photosynthetic photosystems, electron transport chains of plastids and mitochondria, and the structural and functional roles for iron in many critical proteins. Given the connection between iron demands and light-dependent processes such as photosynthesis, as well as the interplay between light and iron, there is a need for finely tuned co-regulation of light and iron acclimation responses to optimize photosynthesis and minimize potential dangerous interactions between iron and light. Such regulation is critical for balancing light and nutrient availability in the coordination of light-dependent aspects of organismal fitness. To accomplish this regulation, there is molecular crosstalk and/or common effectors in light signaling and iron acclimation control. We explore known paradigms that are central to light–iron interactions and the associated regulation of fitness in photosynthetic organisms.