Carotenoids are important terpenoid compounds in plants, playing a crucial role in the formation of visual, sensory, and nutritional quality in horticultural crops. As a key rate-limiting enzyme in the carotenoid biosynthetic pathway, the expression of the gene encoding phytoene synthase (PSY) plays a pivotal role in regulating carotenoid accumulation in horticultural crops. This review systematically summarizes the diversification of the PSY gene family and their tissue-specific expression patterns across different crops, revealing the evolutionary basis of their functional diversity. Furthermore, this review elaborates on the multi-level regulatory network governing PSY: At the transcriptional level, various transcription factors precisely regulate its spatiotemporal expression by binding to the PSY promoter region, epigenetic mechanisms dynamically modulate PSY accessibility by altering chromatin states; at the post-transcriptional level, alternative splicing and trans-splicing generate functionally distinct transcripts, enabling fine-tuning of PSY transcript abundance and translation efficiency; at the post-translational level, the OR chaperone and Clp protease system antagonistically regulate PSY protein stability, while ubiquitination precisely controls its degradation rate; and subcellular localization mechanism ensures efficient catalysis within plastids. In addition, PSY expression and activity are cross-regulated by environmental factors such as light and temperature, as well as hormonal signals including ethylene and abscisic acid, forming a complex regulatory network. Current research still faces several challenges. Most studies focus on a few model crops, while regulatory pathway differences among species remain poorly understood. In addition, the interaction networks between phytoene synthase (PSY) and its upstream and downstream regulatory factors, as well as the mechanisms underlying metabolic channeling, require further in-depth investigation. In the future, research should employ synthetic biology tools to rationally design PSY for improved stability and catalytic efficiency, utilize artificial intelligence and multi-omics integration to identify key regulatory nodes, and implement gene editing and metabolic engineering strategies to achieve precise enhancement of carotenoid content in horticultural crops.
