Distinct contributions of cryptochromes and UVR8 to blue light signaling and root development in Arabidopsis

Plants integrate spectral cues through interconnected photoreceptor networks, yet how blue light receptors interact with UV-B signaling components under mixed light environments remains unresolved. Here, we investigated the functional interplay between cryptochromes (CRY1/CRY2) and UV RESISTANCE LOCUS 8 (UVR8) in regulating transcriptional and developmental responses in Arabidopsis under monochromatic and mixed light conditions. Using photoreceptor mutants across L er and Ws backgrounds, we combined short-term blue light exposure, monochromatic treatments, and variable blue:red (B:R) ratios to assess gene expression, hypocotyl elongation, root growth, and biomass accumulation. CRYs emerged as the primary mediators of blue light responses, controlling induction of photomorphogenic genes ( HY5 , CHS , RUP2 ) and inhibiting hypocotyl elongation. Loss of CRY function abolished transcriptional activation and growth inhibition, confirming their central regulatory role. In contrast, UVR8 was largely dispensable for primary blue light responses but acted as a context-dependent modulator, with effects varying by genetic background, light quality, and developmental output. Notably, UVR8 contributed to root growth regulation and auxin-related transcription, particularly under red-enriched or mixed spectra. The cry1cry2uvr8 triple mutant revealed non-additive and compensatory interactions, indicating functional redundancy between CRYs and UVR8. These findings demonstrate that coordinated CRY-UVR8 crosstalk enables flexible tuning of plant development across dynamic light environments, with implications for optimizing spectral conditions in controlled environment agriculture.