The role of light in shaping plant growth: mechanisms of photomorphogenesis and hormonal integration during seedling development

Seed germination: light-hormone-epigenome crosstalk at the dormancy-to-growth transition

Seed dormancy and germination represent a critical developmental transition that determines plant fitness, ecological adaptation, and agricultural productivity. This switch is governed by the integration of environmental cues with endogenous hormonal networks, most notably the antagonistic balance between abscisic acid (ABA), which enforces dormancy, and gibberellins (GA), which promote germination. Among environmental signals, light acts as a central informational cue regulating germination timing through phytochrome-mediated pathways. A key component of this network is PHYTOCHROME-INTERACTING FACTOR 1 (PIF1), a transcriptional regulator that maintains dormancy in darkness by promoting ABA biosynthesis and signaling while suppressing GA accumulation. Light perception through phytochromes triggers rapid degradation of PIF1, leading to a hormonal reprogramming that shifts the balance toward GA dominance and initiates germination. Crucially, this light-hormone signaling module is strongly integrated with epigenetic regulation, where chromatin remodeling, DNA methylation, histone modifications, and small RNAs dynamically regulate the accessibility of key dormancy- and germination-related genes. This multilayered regulatory architecture enables environmental inputs to be converted into stable or reversible developmental states during the dormancy-to-growth transition. In this review, we synthesize current advances in understanding how light signaling interfaces with hormonal and epigenetic pathways to control seed fate decisions. We further highlight how additional environmental cues, including temperature, nitrate availability, and smoke-derived signals, converge on the ABA–GA regulatory axis to fine-tune germination responses. Additionally, we discuss emerging mechanistic gaps and translational opportunities for improving seed performance, reducing pre-harvest sprouting (PHS), and enhancing crop resilience under changing climatic conditions. Collectively, we propose an integrated framework in which light, hormonal, and epigenetic networks function as a coordinated regulatory system ensuring germination occurs only under favorable environmental conditions.

Seeds and Seedlings: How Arabidopsis thaliana integrates light signalling in its earliest life stages.

Photoreceptors as Central Hubs of Developmental Plasticity and Environmental Adaptation.

Plant photoreceptors are well known for their roles in light-dependent developmental processes such as photomorphogenesis, shade avoidance, and circadian regulation. These canonical functions involve light perception through specific receptors, including phytochromes and cryptochromes, and downstream transcriptional reprogramming mainly in the context of early seedling growth. Beyond their classical roles, recent studies have revealed that photoreceptors also act as integrators of diverse environmental signals, contributing to abiotic stress adaptation, root development, and vascular differentiation. Notably, these non-canonical functions involve direct protein-protein interactions, post-translational modifications, and hormonal crosstalk, enabling photoreceptors to respond to environmental cues beyond light. Moreover, photoreceptor activity has been detected in tissues with limited or no light exposure, such as roots and adult vascular tissues, where they contribute to developmental and stress-responsive processes. In selected cases, particularly for phyB, non-light stress-related signals have been reported to modulate photoreceptor stability or subnuclear organization, suggesting that the functional repertoire of photoreceptors may extend beyond traditional photoperception. This review summarizes emerging insights into the non-canonical functions of photoreceptors in abiotic stress adaptation, root and vascular development, with particular focus on light-independent signaling, root-local photoreceptor activity and non-cell autonomous light signaling. By integrating recent findings, we aim to provide a broader perspective on how photoreceptors serve as central regulators of plant plasticity in response to both light and non-light environmental factors, spanning from early to adult developmental programs.

Turning over a green leaf: integrating light signals towards chloroplast establishment.

Light is indispensable for transitioning from a heterotrophic to a photoautotrophic state. Etiolated seedlings, developed in darkness, are primed for rapid chloroplast development upon light exposure. In this transition, dark-adapted etioplasts differentiate into functional chloroplasts through a tightly regulated process controlled at multiple levels. Light steers gene transcription and translation, as well as post-translational modifications of both plastid- and nuclear-encoded chloroplast and photosynthetic proteins. Light is sensed not only by dedicated nuclear photoreceptors like phytochromes and cryptochromes, but also directly by plastids themselves. For example, incoming light drives chlorophyll metabolism, which initiates a cascade of structural and metabolic changes. The shaping of functional chloroplasts involves adjustments to the membrane lipid composition and the incorporation of photosynthetic proteins, contributing to the internal membrane structure for the buildup of the photosystems. In this update, we review our current understanding of integrated light signals in plastids and the nucleus that drive the multi-level transition of non-photosynthetic etioplasts towards fully functioning chloroplasts.

Photoperiod, Light Quality, and Intensity: Integrated Signalling and Hormonal Crosstalk in the Spatiotemporal Control of Plant Vascular Development.

Light acts as both the primary energy source for photosynthesis and a pivotal environmental signal that orchestrates plant growth and developmental transitions. The plant vascular system, comprising xylem, phloem, and cambium, dynamically adjusts its development in response to light intensity, quality, and photoperiod. This review synthesises current knowledge on how light signalling regulates cambial activity, xylem and phloem differentiation, and secondary cell wall formation. We elaborate on the molecular interplay between light signalling components and key vascular developmental regulators. Understanding these mechanisms is crucial for deciphering plant adaptation to variable light environments and holds significant potential for enhancing crop resilience and woody biomass yield in the context of global climate change.

Duet between sugars and hormones: The molecular dialogue fine-tuning hypoxia acclimation in plants.

Hypoxic conditions caused by submergence or soil waterlogging constrain plant growth and productivity. To survive, plants coordinately reprogram both sugar metabolism and phytohormone signaling to trigger adaptive responses; yet, the integrative regulatory frameworks governing this interaction remain unresolved. Here, we synthesize current knowledge on how sugars, acting as both metabolites and signals, intersect with phytohormone networks to regulate growth and survival under low-oxygen stress. Under hypoxia, ethylene and auxin reshape root architecture, while cytokinin mediates sugar-dependent regulation of shoot branching to optimize resource allocation. The dynamic interplay between abscisic acid and sugars is central to maintaining energy balance under cyclic day-night hypoxia. This interaction modulates the stomatal aperture, facilitates controlled starch degradation, and coordinates sucrose transport to sustain metabolism. Furthermore, crosstalk between primary sugars, gibberellin, and brassinosteroid fine-tunes critical developmental transitions, including seed germination and internode elongation. Although individual signaling pathways under hypoxia have been well studied, their integration via sugar-hormone crosstalk remains elusive. To address these issues, we propose integrating synthetic low-oxygen sensors that initially detect hypoxic stress with engineered sugar-hormone balancing circuits that subsequently fine-tune metabolic and hormonal responses, thereby creating closed-loop feedback systems for adaptive stress resilience. Such systems could enable "Sensing, Metabolism, Adaptation, and Regulation Technology" (SMART) crops to autonomously sense and adapt to hypoxia stress. By synthesizing current knowledge and existing gaps, our work proposes future directions to advance the development of hypoxia-resilient crops through optimizing growth and yield stability under stress.