A long-lived signal for long-lived plants: Phytomelatonin and stress resilience in woody species

Woody plants experience recurrent drought, salinity, toxic-metal exposure, heat, nutrient limitation, and pathogen pressure across seasons and decades, yet the molecular systems that sustain durable stress resilience in these perennial species remain incompletely resolved. Phytomelatonin has been discovered as an emerging molecule that links organellar redox buffering with stress signaling metabolism, immunity, and resilience. In this review, we synthesize current evidence that melatonin biosynthesis, together with downstream hydroxymelatonin metabolism, shapes stress-responsive indoleamine flux in trees and woody crops. We highlight how stress-regulated melatonin production is integrated with ROS–Ca²⁺ signaling, transcriptional regulation, phytohormone crosstalk, antioxidant defense, phenylpropanoid metabolism, autophagy, ion and nutrient homeostasis, and immune priming. We further emphasize functions that are especially relevant to perennial life histories of woody species, including vascular and hydraulic protection, secondary-wall reinforcement, cambial and long-lived leaf resilience, root–microbiome interactions, phloem-associated defense, and postharvest quality maintenance. Although evidence from apple, poplar, citrus, pear, willow, kiwifruit, and other woody systems supports melatonin as a multifunctional resilience module, major gaps remain in receptor-level signaling, compartment-resolved flux, derivative-specific function, long-distance transport, and multi-year field validation. We propose that woody plants may use just-in-time melatonin regulation and derivative buffering to balance rapid stress protection with sustained growth and reproductive performance. Together, current findings position phytomelatonin as a promising regulatory “hub” for understanding and improving stress resilience in forestry and perennial fruit production under intensifying environmental stress.