Integrated transcriptomics and metabolomics analyses reveal the molecular mechanisms of red-light on carotenoids biosynthesis in tomato fruit

Carotenoids are the main pigments responsible for the coloration and account for the major antioxidant activity of tomato(Solanum lycopersicum L.)fruit.Significant increments in total carotenoids and lycopene levels were observed in tomato fruit illuminated by red light relative to white light in previous studies,but the mechanism of carotenoid biosynthesis regulated by red light is stll unclear.In the present study,the influence of red light on carotenoid biosynthesis in postharvest tomato fruit was conducted using targeted metabolomics and transcriptomic methods.A total of 25 differentially accumulated carotenoids and 1939 differentially expressed genes were isolated and identified.The results illustrated that the contents of phytoene and lycopene were considerably higher in fruit treated with red light than those with white light at 12 h.These differentially expressed genes are mainly enriched in plant hormone signal transduction,photosynthesis,secondary metabolite biosynthesis,and plant circadian rhythm.Moreover,from the results of coexpression network analysis,15 transcription factors from red light-treated fruit were screened;among these,transcription factors of SIERF4,SlbHLH93 and SllAA29,which are involved in signal transduction of light and hormones,respectively,may also play important roles in carotenoid biosynthesis regulated by red light in tomato fruit.It is concluded that red light enhanced carotenoid biosynthesis in postharvest tomato fruit and the mechanisms of enhanced carotenoid biosynthesis were not only associated with the direct regulation by red light signalling,but also with the indirect regulation by hormonal signalling.