Carotenoids are important isoprenoids produced in the plastids of photosynthetic organisms that play key roles in photoprotection and antioxidative processes. β-Carotene is generated from lycopene by lycopene β-cyclase (LCYB). Previously, we demonstrated that the introduction of the Daucus carota (carrot) DcLCYB1 gene into tobacco (cv. Xanthi) resulted in increased levels of abscisic acid (ABA) and especially gibberellins (GAs), resulting in increased plant yield. In order to understand this phenomenon prior to exporting this genetic strategy to crops, we generated tobacco (Nicotiana tabacum cv. Petit Havana) mutants that exhibited a wide range of LCYB expression. Transplastomic plants expressing DcLCYB1 at high levels showed a wild-type-like growth, even though their pigment content was increased and their leaf GA1 content was reduced. RNA interference (RNAi) NtLCYB lines showed different reductions in NtLCYB transcript abundance, correlating with reduced pigment content and plant variegation. Photosynthesis (leaf absorptance, Fv/Fm, and light-saturated capacity of linear electron transport) and plant growth were impaired. Remarkably, drastic changes in phytohormone content also occurred in the RNAi lines. However, external application of phytohormones was not sufficient to rescue these phenotypes, suggesting that altered photosynthetic efficiency might be another important factor explaining their reduced biomass. These results show that LCYB expression influences plant biomass by different mechanisms and suggests thresholds for LCYB expression levels that might be beneficial or detrimental for plant growth.

• Klíčová slova
• Nicotiana tabacum cv. Petit Havana, RNAi, biomass, carotenoids, lycopene β-cyclase, photosynthesis, phytohormones, transplastomic, β-Carotene,
• MeSH
• geneticky modifikované rostliny genetika   metabolismus   MeSH
• intramolekulární lyasy * genetika   metabolismus   MeSH
• karotenoidy MeSH
• regulace genové exprese u rostlin MeSH
• rostlinné proteiny genetika   metabolismus   MeSH
• tabák * genetika   metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• intramolekulární lyasy * MeSH
• karotenoidy MeSH
• lycopene cyclase-isomerase MeSH Prohlížeč
• rostlinné proteiny MeSH

Thraustochytrids (phylum: Labyrinthulomycota) are nonphotosynthetic marine protists. Some thraustochytrids have crtIBY, a trifunctional fusion gene encoding a protein capable of β-carotene biosynthesis from geranylgeranyl pyrophosphate. Here we show that crtIBY is essential in, and encodes the sole pathway for, carotenoid biosynthesis in the thraustochytrid Aurantiochytrium limacinum ATCC MYA-1381. We explore the evolutionary origins of CrtIBY and discover that the closest related protein domains are present in a small but diverse group of other heterotrophic protists, including the apusomonad Thecamonas trahens and the dinoflagellates Oxyrrhis marina and Noctiluca scintillans. Each organism within this cluster also contains one or more β-carotene 15-15' oxygenase genes (blh and rpe65), suggesting that the acquisition of β-carotene biosynthesis genes may have been related to the production of retinal. Our findings support a novel origin of eukaryotic (apo)carotenoid biosynthesis by horizontal gene transfer from Actinobacteria, Bacteroidetes, and/or Archaea. This reveals a remarkable case of parallel evolution of eukaryotic (apo)carotenogenesis in divergent protistan lineages by repeated gene transfers.

• Klíčová slova
• carotenoid oxygenase, lycopene cyclase, phylogenetics, phytoene desaturase, phytoene synthase, thraustochytrids,
• MeSH
• Bacteria genetika   MeSH
• beta-karoten genetika   MeSH
• Heterokontophyta * MeSH
• karotenoidy * MeSH
• přenos genů horizontální MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH
• Názvy látek
• beta-karoten MeSH
• karotenoidy * MeSH

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.

• Klíčová slova
• Nicotiana tabacum, ABA, biomass, carotenoids, gibberellins, photosynthesis, β-carotene,
• MeSH
• fotosyntéza genetika   fyziologie   MeSH
• geneticky modifikované rostliny MeSH
• gibereliny metabolismus   MeSH
• karotenoidy metabolismus   MeSH
• kyselina abscisová metabolismus   MeSH
• metabolické sítě a dráhy genetika   MeSH
• mrkev obecná genetika   MeSH
• regulace genové exprese u rostlin genetika   MeSH
• regulátory růstu rostlin metabolismus   MeSH
• rostlinné geny genetika   fyziologie   MeSH
• rostlinné proteiny genetika   fyziologie   MeSH
• tabák anatomie a histologie   růst a vývoj   metabolismus   fyziologie   MeSH
• upregulace MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• gibereliny MeSH
• karotenoidy MeSH
• kyselina abscisová MeSH
• regulátory růstu rostlin MeSH
• rostlinné proteiny MeSH