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 and 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.