Manipulating levels of carotenoid-related enzymes and transcription factors in tomato (Solanum lycopersicum L.)
[eng] Carotenoids are essential isoprenoids in plants, primarily required for photoprotection. However, their functions vary depending on the plant species and organ, serving as pigments in many flowers and fruits and as precursors of hormones such as abscisic acid (ABA) and strigolactones (SLs) in...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2025 |
| País: | España |
| Institución: | Universidad de Barcelona |
| Repositorio: | Dipòsit Digital de la UB |
| OAI Identifier: | oai:dnet:ubarcelona__::70ce503ff60e376dd93fe2d98550855c |
| Acceso en línea: | https://hdl.handle.net/2445/228860 https://hdl.handle.net/10803/697226 |
| Access Level: | acceso embargado |
| Palabra clave: | Carotenoides Isoprenoides Antioxidants Factors de transcripció Biosíntesi Carotenoids Isopentenoids Transcription factors Biosynthesis |
| Sumario: | [eng] Carotenoids are essential isoprenoids in plants, primarily required for photoprotection. However, their functions vary depending on the plant species and organ, serving as pigments in many flowers and fruits and as precursors of hormones such as abscisic acid (ABA) and strigolactones (SLs) in other tissues. In humans, dietary carotenoids serve as important sources of antioxidant compounds and vitamin A. Therefore, carotenoid biofortification is a key strategy to enhance food security and improve nutrition. Carotenoids are present at relatively high levels in the fruit of agriculturally important species such as tomato (Solanum lycopersicum L.). However, our knowledge of how isoprenoid precursors are channeled into the carotenoid pathway in fruits and other organs of this important crop is still very limited. Phytoene synthase (PSY) is a key enzyme that produces phytoene (the first intermediate in the carotenoid pathway) from geranylgeranyl pyrophosphate (GGPP). In the previous step, GGPP synthases (GGPPS) synthesize GGPP from the universal isoprenoid precursors isopentenyl pyrophosphate and dimethylallyl pyrophosphate. Tomato has three genes encoding isoforms of GGPPS (here referred to as SlG1, SlG2, and SlG3) and PSY (PSY1, PSY2, and PSY3). In the first part of this thesis, we used previously generated tomato edited lines defective in individual GGPPS or PSY isoforms to generate double mutant combinations. The main objective was to understand what GGPPS-PSY pairs regulated the channeling of isoprenoid precursors into the carotenoid pathway in different organs of the tomato plant, including leaves, flowers and fruits (as the SlG1-PSY3 tandem had been previously shown to be involved in SL production in roots). The generation and analysis of double mutants revealed a major role for SlG3 in providing GGPP to PSY2 for carotenoid production in the leaf, while SlG2 and PSY1 appeared to be most relevant in flower and fruit tissues. In the second chapter of the thesis, we aimed at editing the tomato gene encoding HY5, a transcription factor shown to activate carotenoid biosynthesis in many plant systems. HY5 is accumulated in the light but degraded in the dark or in the shade via interaction with the E3 ubiquitin ligase COP1. To increase HY5 activity, we generated tomato lines with a truncated version of HY5 that is unable to interact with COP1. The resulting HY5 gain-of-function lines (referred to as slhy5-D lines) exhibited shorter hypocotyls, epicotyls and higher leaf anthocyanin content compared to their respective backgrounds, whereas Western blot analysis confirmed increased stability and abundance of the mutant HY5 protein in different light conditions. Strikingly, slhy5-D lines did not show substantially increased levels of carotenoids in leaves or fruits. We further investigated the phenotype of slhy5-D lines considering that increased HY5 activity might result in shade tolerance. The presence of neighboring plants results in a decreased ratio of red to far-red light (low R:FR) resulting from the preferential use of R for photosynthesis and the reflection or filtering of FR. Shade associated to vegetation proximity can be simulated in the lab by enriching white light (W, high R:FR) with FR (W+FR, low R:FR). All tomato accessions analyzed were found to elongate and reduce their photosynthetic pigment levels (including carotenoids) in response to W+FR illumination compared to W-exposed controls. When exposed to W+FR, slhy5-D lines displayed partial shade tolerance compared to their unedited parental lines, as deduced from attenuated plant elongation. However, no effects were observed in carotenoid levels. Finally, in the last chapter of the thesis, we investigated whether alterations in other molecular components resulting in shade tolerance could prevent the degradation of carotenoids associated to low R:FR signaling. Specifically, we carried out an untargeted approach to look for shade-tolerant mutants in collections of tomato landraces and introgression lines (ILs). As a result, we identified an introgression line (IL2-2) as tolerant to W+FR conditions in terms of elongation. In this line, photosynthetic carotenoid levels did not decrease under W+FR compared to W at the seedling stage, but the phenotype was not preserved in adult plants. This line exhibited altered auxin homeostasis and reduced expression of auxin-responsive genes under simulated proximity shade. Notably, IL2-2 also showed improved yield performance under high-density planting conditions in open-field trials. |
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