WRKY transcription factors in horticultural crops: regulating quality traits and fruit stress responses.

WRKY transcription factors regulate pigments, sugars, organic acids, aroma compounds, ripening, texture, and stress tolerance, offering promising targets for improving horticultural crop quality and postharvest performance. WRKY transcription factors (TFs) belong to one of the largest families of regulatory proteins in plants, with multifaceted roles in growth, development, and stress responses. This review summarizes the diverse functions of WRKY TFs that regulate key quality traits of horticultural crops, including fruits, vegetables, and ornamentals. We discuss the structural characteristics and classification of WRKY TFs, emphasizing their conserved WRKY domain and W-box binding mechanism. We comprehensively examine how WRKY TFs control critical quality attributes, such as pigment accumulation (anthocyanins, carotenoids, and betalains), organ size, sugar and organic acid contents, aroma-related volatile production, texture, and fruit ripening, by directly modulating structural genes and interacting with other TFs. Additionally, we explore the involvement of WRKY TFs in fruit responses to biotic stresses (e.g., pathogen infections) and abiotic stresses (e.g., chilling) as well as fruit browning. We also highlight their effects on hormone signaling and defense pathways. Despite significant progress in identifying WRKY TFs associated with quality traits through high-throughput approaches, the functional characterization of many of these TFs remains incomplete. Future research directions include using advanced genetic engineering tools, such as CRISPR/Cas9, to validate functions, elucidate complex regulatory networks involving WRKY TFs and their target genes, and explore upstream regulatory mechanisms. The results of this research will facilitate the development of improved horticultural cultivars with enhanced quality, stress tolerance, and extended shelf life, ultimately contributing to food security and market competitiveness.