Group VII ethylene response factors forming distinct regulatory loops mediate submergence responses

A mechanistic integration of hypoxia signaling with energy, redox, and hormonal cues

Oxygen deficiency (hypoxia) occurs naturally in many developing plant tissues but can become a major threat during acute flooding stress. Consequently, plants as aerobic organisms must rapidly acclimate to hypoxia and the associated energy crisis to ensure cellular and ultimately organismal survival. In plants, oxygen sensing is tightly linked with oxygen-controlled protein stability of group VII ETHYLENE-RESPONSE FACTORs (ERFVII), which, when stabilized under hypoxia, act as key transcriptional regulators of hypoxia-responsive genes (HRGs). Multiple signaling pathways feed into hypoxia signaling to fine-tune cellular decision-making under stress. First, ATP shortage upon hypoxia directly affects the energy status and adjusts anaerobic metabolism. Secondly, altered redox homeostasis leads to reactive oxygen and nitrogen species (ROS and RNS) accumulation, evoking signaling and oxidative stress acclimation. Finally, the phytohormone ethylene promotes hypoxia signaling to improve acute stress acclimation, while hypoxia signaling in turn can alter ethylene, auxin, abscisic acid, salicylic acid, and jasmonate signaling to guide development and stress responses. In this Update, we summarize the current knowledge on how energy, redox, and hormone signaling pathways are induced under hypoxia and subsequently integrated at the molecular level to ensure stress-tailored cellular responses. We show that some HRGs are responsive to changes in redox, energy, and ethylene independently of the oxygen status, and we propose an updated HRG list that is more representative for hypoxia marker gene expression. We discuss the synergistic effects of hypoxia, energy, redox, and hormone signaling and their phenotypic consequences in the context of both environmental and developmental hypoxia.

Advances in plant oxygen sensing: endogenous and exogenous mechanisms

Oxygen is essential for the biochemical processes that sustain life in eukaryotic organisms. Although plants produce oxygen through photosynthesis, they often struggle to survive in low-oxygen environments, such as during flooding or submergence. To endure these conditions, they must reprogram their developmental and metabolic networks, and the adaptation process involves the continuous detection of both exogenous hypoxic signals and endogenous oxygen gradients. Recent research has significantly advanced our understanding of how plants respond to both endogenous and exogenous hypoxia signals. In this review, we explore advancements in both areas, comparing them to responses in animals, with a primary focus on how plants perceive and respond to exogenous hypoxic conditions, particularly those caused by flooding or submergence, as well as the hypoxia signaling pathways in different crops. Additionally, we discuss the interplay between endogenous and exogenous hypoxia signals in plants. Finally, we discuss future research directions aimed at improving crop resilience to flooding by integrating the perception and responses to both endogenous and exogenous signals. Through these efforts, we aspire to contribute to the development of crop varieties that are not only highly resistant but also experience minimal growth and yield penalties, thereby making substantial contributions to agricultural science.