Advances in carotenoid and apocarotenoid metabolisms and functions in plants.

Carotenoids and their derivative apocarotenoids are diverse isoprenoid metabolites vital to plants and critical to humans. Recent discoveries have expanded our understanding of the intricate mechanisms modulating their metabolism and revealed their new functions in plants. Many new regulators and regulatory modules that potentially link carotenoid metabolism with developmental, hormonal, and environmental cues have been unraveled. Emerging evidence also reveals the importance of loss of photosynthetic competence for carotenoid accumulation in chromoplasts. Moreover, apocarotenoids rapidly surface as important regulatory metabolites and signals involved in plant growth and development, stress responses, and communication. In this review, we focus on the latest research in elucidating multifaceted regulatory mechanisms governing carotenoid and apocarotenoid metabolism in plants, provide insights into the differentiation of plastids specialized for carotenoid accumulation, and offer an update on the discoveries and functions of bioactive apocarotenoids. Future research directions to address remaining knowledge gaps are outlined. Collectively, we aim to highlight major advances and exciting discoveries in the field, with the goal of enabling precise and effective augmentation of carotenoids and apocarotenoids with improved nutritional quality, growth, and stress tolerance in crops.