This not only proves that limitations for crop productivity, caused by the adaptation of plants to the terrestrial 24-h day/night cycle, can be overcome but also opens new research lines in the most important process of photosynthesis. By introgressing the tolerance into modern tomato F 1 hybrid lines, we achieve up to a 20% yield increase. Genetic evidence, RNAseq data, silencing experiments and sequence analysis all point to the type III Light Harvesting Chlorophyll a/b Binding protein 13 ( CAB-13) gene as a major factor responsible for the tolerance. In this study, we locate CL tolerance, mapping to the lower arm of chromosome 7, in eight wild tomato accessions. Under greenhouse conditions, a tomato crop simulation model, TOMSIM 22, predicted that a hypothetical CL-tolerant tomato genotype, would yield between 22 and 26% more fruits when using supplementary lighting for 24 h per day (CL) in comparison with using supplementary lighting only for 18 h per day during daytime under Dutch greenhouse conditions 23. Understanding why CL injures tomato plants is not only valuable for fundamental research but also has potential applications, as tomato is the most important vegetable crop worldwide. We have proposed that a combination of these components could induce the injury rather than a particular one on its own 13. However, concluding which component induces the injury is not simple because, in most cases, CL affects all four components simultaneously. Finally, the role of circadian asynchrony on the CL-induced injury has been examined and/or suggested in several papers 13, 18, 19, 20, 21. Addition of far-red light to the CL treatment reduced injury symptoms 17, suggesting an involvement of phytochromes. The photoinhibition and adaptation of photosystems I and II (PSI and PSII) have been studied in CL-grown tomatoes by ref. For instance, carbohydrate accumulation, which presumably results from continuous energy supply for photosynthesis, has been regarded for a long time as a potential trigger of CL-induced injury 1, 7, 13, 16. The importance of these four components on the CL-induced injury has been previously investigated in several experimental setups. In contrast to natural day/night cycles, CL implies continuous energy supply for photosynthesis, continuous photooxidative pressure, continuous signalling to the photoreceptors and a mismatch between the internal circadian clock frequency and the external light/dark cycle known as circadian asynchrony 13. More than eight decades after the original discovery, however, the physiological basis of this CL-induced injury remains poorly understood. Hence, the high sensitivity to CL of tomato, an emerging model organism for the Solanaceae family and fleshy fruited plants 12, is intriguing and has motivated plenty of research efforts (see Supplementary Table 1 for complete literature list and for reviews see refs 13, 14, 15). However, many other plant species, like the model plant Arabidopsis ( Arabidopsis thaliana) 2, 3, pepper ( Capsicum annuum) 4, 5, 6, 7, 8, lettuce ( Lactuca sativa) 1, 9 and rose ( Rosa x hybrida) 10, 11 are not injured by CL. Experiments in the 1920s revealed that tomato ( Solanum lycopersicum) plants, when grown under continuous light (CL), develop a potentially lethal injury characterized by mottled leaf chlorosis and necrosis 1.
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