Shedding light on tocopherol biosynthesis regulation in tomato fruits

Due to the high consumption and biochemical composition, tomato fruit is an important source of antioxidant compounds for human diet, such as carotenoids, ascorbic acid and tocopherols (vitamin E, VTE). Besides its nutritional value, tocopherols are essential part of the photosynthetic machinery, affecting plant adaptability to light conditions and tomato fruit productivity. Tocopherols are synthesized in the plastids and light has a strong role in regulating chloroplast maintenance and activity; therefore, this environmental cue is expected to affect the accumulation of plastid-derived nutraceutical compounds, as already demonstrated for carotenoids. To understand the interplay between light and VTE accumulation, we investigated whether light regulates VTE biosynthesis. First, we found that tocopherol levels are altered in fruits from mutants impaired in light perception, as well as in fruits ripened under different light conditions. Moreover, the transcript profile of key genes of VTE biosynthesis, such as GGDR, VTE2, VTE3, VTE5 and VTE6, suggested that the light influence on fruit tocopherol content relies on the transcriptional regulation of these genes. As PHYTOCHROME INTERACTING FACTORS (PIFs) and HYPOCOTYL ELONGATED 5 (HY5) are the main transcription factors (TFs) involved in light-mediated signaling, we performed a de novo search for cis-motifs on promoter regions of VTE biosynthetic genes. Motifs recognized by both TFs were found in all the promoters analyzed. Thus, we investigated the TF-promoter interactions by transactivation assays and ChIP-qPCR analysis. Overall, our results suggest that TFs involved in light-signaling transduction regulate VTE biosynthesis by direct interaction with the promoters of VTE biosynthetic enzyme- encoding genes.