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Photosynthesis is one the most important chemical reaction in plants, and it is the ultimate energy source of any living organisms. The light and dark reactions are two essential phases of photosynthesis. Light reaction harvests light energy to synthesize ATP and NADPH through an electron transport chain, and as well as giving out O2; dark reaction fixes CO2 into six carbon sugars by utilizing NADPH and energy from ATP. Subsequently, plants convert optical energy into chemical energy for maintaining growth and development through absorbing light energy. Here, firstly, we highlighted the biological importance of photosynthesis, and hormones and metabolites, photosynthetic and regulating enzymes, and signaling components that collectively regulate photosynthesis in tomato. Next, we reviewed the advances in tomato photosynthesis, including two aspects of genetic basis and genetic improvement. Numerous genes regulating tomato photosynthesis are gradually uncovered, and the interaction network among those genes remains to be constructed. Finally, the photosynthesis occurring in fruit of tomato and the relationship between photosynthesis in leaf and fruit were discussed. Leaves and fruits are photosynthate sources and sinks of tomato respectively, and interaction between photosynthesis in leaf and fruit exists. Additionally, future perspectives that needs to be addressed on tomato photosynthesis were proposed.

Abstract Background Ascorbic acid (Vitamin C, AsA) is an antioxidant metabolite involved in plant development and environmental stimuli. AsA biosynthesis has been well studied in plants, and MIOX is a critical enzyme in plants AsA biosynthesis pathway. However, Myo-inositol oxygenase (MIOX) gene family members and their involvement in AsA biosynthesis and response to abiotic stress remain unclear. Results In this study, five tomato genes encoding MIOX proteins and possessing MIOX motifs were identified. Structural analysis and distribution mapping showed that 5 MIOX genes contain different intron/exon patterns and unevenly distributed among four chromosomes. Besides, expression analyses indicated the remarkable expression of SlMIOX genes in different plant tissues. Furthermore, transgenic lines were obtained by over-expression of the MIOX4 gene in tomato. The overexpression lines showed a significant increase in total ascorbate in leaves and red fruits compared to control. Expression analysis revealed that increased accumulation of AsA in MIOX4 overexpression lines is possible as a consequence of the multiple genes involved in AsA biosynthesis. Myo inositol (MI) feeding in leaf and fruit implied that the Myo-inositol pathway improved the AsA biosynthesis in leaves and fruits. MIOX4 overexpression lines exhibited a better light response, abiotic stress tolerance, and AsA biosynthesis capacity. Conclusions These results showed that MIOX4 transgenic lines contribute to AsA biosynthesis, evident as better light response and improved oxidative stress tolerance. This study provides the first comprehensive analysis of the MIOX gene family and their involvement in ascorbate biosynthesis in tomato.