Decoding the Multifunctionality of B-Box Proteins: Bridging Light, Stress and Developmental Networks in Diverse Plant Species.

Abstract

B-box (BBX) transcription factors are emerging as pivotal regulators of environmental adaptation and developmental plasticity in plants. These proteins act at the intersection of light, hormonal and stress signalling networks to modulate key processes, including photomorphogenesis, circadian rhythm regulation, abiotic and biotic stress responses, anthocyanin biosynthesis and flowering time control. Recent studies in various model species and crops have revealed that BBX proteins can function as both activators and repressors of transcription, often by directly interacting with key regulators such as HY5, PRR9/7 and MYC2. These interactions enable BBX factors to fine-tune gene expression in response to dynamic environmental conditions. Functionally, BBX proteins orchestrate light-responsive development, enhance tolerance to drought, salinity, and pathogens via hormonal and reactive oxygen species (ROS)-mediated pathways, and regulate secondary metabolism linked to pigment accumulation. Their roles in reproductive development, particularly in controlling flowering time and vegetative-reproductive phase transitions, position them as promising targets for crop improvement. Despite growing insight, key knowledge gaps remain. The mechanistic basis of BBX duality, their post-translational regulation and their integration within broader transcriptional and chromatin networks are still poorly understood. Additionally, BBX-mediated signalling remains understudied in monocots, wild relatives and under complex field conditions. This review summarizes the latest mechanistic and evolutionary insights into BBX transcription factors, emphasizing their functional diversity, context-dependent regulation, and applications in precision breeding. By highlighting both translational applications and unresolved challenges, we propose future directions for using BBX proteins to design of climate-resilient, high-performance crops.