Because carotenoids act as accessory pigments in photosynthesis, play a key photoprotective role and are of major nutritional importance, carotenogenesis has been a target for crop improvement. Although carotenoids are important precursors of phytohormones, previous genetic manipulations reported little if any effects on biomass production and plant development, but resulted in specific modifications in carotenoid content. Unexpectedly, the expression of the carrot lycopene β-cyclase (DcLCYB1) in Nicotiana tabacum cv. Xanthi not only resulted in increased carotenoid accumulation, but also in altered plant architecture characterized by longer internodes, faster plant growth, early flowering and increased biomass. Here, we have challenged these transformants with a range of growth conditions to determine the robustness of their phenotype and analyze the underlying mechanisms. Transgenic DcLCYB1 lines showed increased transcript levels of key genes involved in carotenoid, chlorophyll, gibberellin (GA) and abscisic acid (ABA) biosynthesis, but also in photosynthesis-related genes. Accordingly, their carotenoid, chlorophyll, ABA and GA contents were increased. Hormone application and inhibitor experiments confirmed the key role of altered GA/ABA contents in the growth phenotype. Because the longer internodes reduce shading of mature leaves, induction of leaf senescence was delayed, and mature leaves maintained a high photosynthetic capacity. This increased total plant assimilation, as reflected in higher plant yields under both fully controlled constant and fluctuating light, and in non-controlled conditions. Furthermore, our data are a warning that engineering of isoprenoid metabolism can cause complex changes in phytohormone homeostasis and therefore plant development, which have not been sufficiently considered in previous studies.

King Abdullah University of Science and Technology Thuwal 23955 6900 Kingdom of Saudi Arabia

Laboratory of Growth Regulators The Czech Academy of Sciences Institute of Experimental Botany and Palacký University Šlechtitelů 27 Olomouc CZ 78371 Czech Republic

Max Planck Institut für Molekulare Pflanzenphysiologie Am Mühlenberg 1 Potsdam Golm 14476 Germany

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Plant J. 2020 Sep;103(6):1965-1966. doi: 10.1111/tpj.14971. PubMed

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Lycopene β-cyclase expression influences plant physiology, development, and metabolism in tobacco plants