CYP72A9 modulates gibberellin abundance in response to osmotic stress

Every year, plants are exposed to increasingly severe environmental stresses. To survive these constant stressors, plants make metabolic tradeoffs to minimize the damage to their subcellular structures. Highly conserved enzymes such as the Cytochrome P450 (CYP) enzyme family are of particular interest in untangling the stress response displayed by a wide variety of plants, because they catalyze a diverse array of biochemical changes. The CYP72A subfamily is involved in a variety of biochemical responses that may include reacting to external stresses. For example, CYP72A9 is a 13-hydroxylase involved in maintaining seed dormancy. This enzyme modulates gibberellins (GAs), which are crucial to plant growth and development. The gene for CYP72A9 is also induced by various abiotic stresses, and may play a role in the metabolic growth-defense tradeoff in plants. Our work tests the hypothesis that CYP72A9 acts as a 13-hydroxylase in response to osmotic stress. We evaluate this hypothesis by measuring the abundance of several GAs when cyp72a9 mutant plants and wild type plants are exposed to mannitol to induce osmotic stress. We find that in stressed conditions the precursors closer to GA4 on the pathway are in very low abundance in wild type, whereas they remain quite high in cyp72a9 mutant plants, supporting the hypothesis that CYP72A9 is critical in the modulation of gibberellic acid.