Phytoglobin 1 in plant hypoxia acclimation and development: integrating oxygen sensing, nitric oxide homeostasis, and redox balance

Hypoxia is integral to the plant life cycle, occurring during both development and environmental stresses such as flooding. The class I phytoglobins (PGB1s) have emerged as important regulators of plant hypoxia responses in both these contexts due to their multifaceted roles in nitric oxide (NO) and reactive oxygen species (ROS) homeostasis, and alternative energy generation. Physiological PGB1 expression overlaps with developmental hypoxic niches, facilitating hypoxic energy generation through the PGB1-NO cycle. Sustained induction of PGB1 by various signals during the progression of a flooding event reflects its important but potentially distinct roles in flooding stress acclimation. These include short-term PGB1-mediated NO scavenging to stabilize ETHYLENE RESPONSE FACTOR VII transcription factors, and in the long-term hypoxic energy generation, oxidative stress mitigation, and maintenance of auxin transport. Here we provide an overview of the current understanding of how PGB1 biochemistry, localization, and regulatory architecture are connected and of relevance for hypoxia acclimation. We highlight key unanswered questions in our understanding of PGB1 biology that will be essential for clarifying its contribution to hypoxia acclimation and plant environmental resilience.