The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.
We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
We are interested in where in or outside the cell the gene product carries out its function.
We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.
Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
The requested target is correctly identified as At3g10230, encoding the chloroplast-targeted lycopene β-cyclase LCY1, also called LCYB and SUPPRESSOR OF ZEAXANTHIN-LESS 1 (SZL1), in Arabidopsis thaliana. This is not a similarly named LCY1 protein from another organism. Authoritative pathway annotation assigns At3g10230 to β-carotene/lycopene β-cyclase, and direct Arabidopsis genetics mapped the szl1 mutation to the LCYB structural gene. Arabidopsis has one principal LCYB gene, further supporting this unambiguous assignment. The supplied UniProt family and domain annotations—lycopene cyclase family, Lycopene_cyclase_b/e, Lycopene_cycl, and an FAD/NAD-binding-like fold—are concordant with the literature. (li2009luteinaccumulationin pages 8-9, ruizsola2012carotenoidbiosynthesisin pages 8-9, dellapenna2006vitaminsynthesisin pages 4-6)
Its primary function is to cyclize the ψ-end groups of all-trans-lycopene into β-ionone rings. Cyclization at both ends produces β-carotene; in cooperation with lycopene ε-cyclase (LCYE), LCYB supplies the β-ring of α-carotene. It therefore controls metabolic partitioning between the β,β-carotenoid branch and the β,ε branch. (li2009luteinaccumulationin pages 8-9, ruizsola2012carotenoidbiosynthesisin pages 8-9)
| Topic | Conclusion | Evidence type / strength | Key quantitative result | Principal source (year; DOI URL) |
|---|---|---|---|---|
| Identity | Q38933 corresponds to Arabidopsis thaliana At3g10230, the single major lycopene β-cyclase gene known as LCY1/LCYB/SZL1; the aliases describe the same target protein. | Direct Arabidopsis evidence—strong: locus annotation plus genetic assignment of the szl1 mutation to the LCYB structural gene. | The hypomorphic szl1 allele carries a conserved Gly→Glu substitution and retains detectable cyclase activity. | DellaPenna & Pogson (2006), https://doi.org/10.1146/annurev.arplant.56.032604.144301; Li et al. (2009), https://doi.org/10.1105/tpc.109.066571 (li2009luteinaccumulationin pages 8-9, dellapenna2006vitaminsynthesisin pages 4-6) |
| Reaction and substrate | LCYB cyclizes the two ψ-ends of all-trans-lycopene, adding two β-rings to yield β-carotene (EC 5.5.1.19). With LCYE acting at one end, LCYB cyclizes the other end of monocyclic δ-carotene to help form α-carotene. | Direct Arabidopsis heterologous evidence plus authoritative pathway synthesis—strong for lycopene→β-carotene; limited kinetic specificity data. Wild-type and hypomorphic Arabidopsis proteins were tested in lycopene-producing E. coli. | Mutant LCYB produced less but detectable β-carotene; with wild-type LCYE, the mutant system produced an α-carotene:β-carotene molar ratio of 4:1. No reliable purified-enzyme Km or kcat was located. | Cunningham et al. (1996), https://doi.org/10.1105/tpc.8.9.1613; Li et al. (2009), https://doi.org/10.1105/tpc.109.066571; Ruiz-Sola & Rodríguez-Concepción (2012), https://doi.org/10.1199/tab.0158 (li2009luteinaccumulationin pages 8-9, ruizsola2012carotenoidbiosynthesisin pages 8-9) |
| Localization | LCYB is a nuclear-encoded plastid/chloroplast precursor with an N-terminal transit peptide; after import, it is associated with chloroplast membranes, with proteomic/pathway evidence favoring the envelope-associated carotenoid machinery. | Arabidopsis proteomic/pathway evidence—moderate; chloroplast localization is well supported, but precise intraplastid topology has less direct experimental resolution. Comparative plant LCYBs also carry approximately 50–100-residue plastid-targeting peptides. | No quantitative Arabidopsis targeting efficiency or membrane-partition coefficient was identified. | Ruiz-Sola & Rodríguez-Concepción (2012), https://doi.org/10.1199/tab.0158; Moreno et al. (2013), https://doi.org/10.1371/journal.pone.0058144 (ruizsola2012carotenoidbiosynthesisin pages 8-9, moreno2013levelsoflycopene pages 1-2) |
| Pathway role | LCYB occupies the first major carotenoid branch point. Two β-cyclizations channel lycopene into β-carotene and the β,β-xanthophylls zeaxanthin, violaxanthin and neoxanthin; cooperation with LCYE supplies the β-ring of α-carotene and thereby supports lutein synthesis. | Direct Arabidopsis mutant/metabolite evidence—strong. Reduced LCYB shifts flux from the β,β branch toward α-carotene/lutein. | szl1 npq1 contained nearly 2× wild-type lutein and an approximately 75% smaller xanthophyll-cycle pool. | Li et al. (2009), https://doi.org/10.1105/tpc.109.066571; Ruiz-Sola & Rodríguez-Concepción (2012), https://doi.org/10.1199/tab.0158 (li2009luteinaccumulationin pages 2-4, ruizsola2012carotenoidbiosynthesisin pages 8-9) |
| Mutant photoprotection phenotype | In zeaxanthin-deficient npq1, partial LCYB impairment raises lutein sufficiently to restore much of rapid, energy-dependent nonphotochemical quenching (qE), demonstrating that altered carotenoid composition—not a second LCYB signaling activity—explains suppression. | Direct Arabidopsis genetics, pigment biochemistry and spectroscopy—strong. | After 5 min of illumination, estimated qE was 1.7 in wild type, 0.8 in npq1 and 1.4 in szl1 npq1. CP24/CP29 lutein radical cations showed a 5-ps rise, approximately 50–60-ps decay, and a peak near 920 nm. | Li et al. (2009), https://doi.org/10.1105/tpc.109.066571 (li2009luteinaccumulationin pages 8-9, li2009luteinaccumulationin pages 2-4) |
| Domains and cofactor | The protein belongs to the plant lycopene-cyclase family and contains the Lycopene_cyclase_b/e region and an FAD/NAD-binding-like fold, consistent with the supplied InterPro/Pfam annotations. Plant LCYB is described as a flavoprotein requiring reduced FAD, although ring formation has no net redox change; the detailed protonation/electron-transfer mechanism remains incompletely resolved. | Family/sequence inference and biochemical review—moderate. Conserved dinucleotide-binding, β-LCY, cyclase and charged motifs align with catalysis and membrane association, but Arabidopsis residue-level structure-function and kinetic data remain sparse. | No experimentally determined Q38933 structure, cofactor stoichiometry or quantitative binding constant was identified. | Ruiz-Sola & Rodríguez-Concepción (2012), https://doi.org/10.1199/tab.0158; Moreno et al. (2013), https://doi.org/10.1371/journal.pone.0058144 (ruizsola2012carotenoidbiosynthesisin pages 8-9, moreno2013levelsoflycopene pages 1-2, moreno2013levelsoflycopene pages 7-9) |
| 2024 application evidence | LCYB remains an engineering target for carotenoid/provitamin-A biofortification and stress resilience. A 2024 study expressed wolfberry LcLCYB in tobacco, increasing carotenoids and improving salt-stress physiology; this supports the application class but is not direct evidence about Arabidopsis Q38933. | Comparative cross-species transgenic evidence—moderate; indirect for Q38933. No 2023–2024 study directly characterizing At3g10230 was identified in the retrieved literature. | LcLCYB overexpression increased β-carotene 3.15-fold and total carotenoids 2.24-fold, with lower H₂O₂ and MDA and higher antioxidant-enzyme activities under NaCl stress. | Li et al. (2024; published May 2024), https://doi.org/10.1038/s41598-024-60848-3 (li2024carotenoidbiosynthesisgenes pages 1-2, li2024carotenoidbiosynthesisgenes pages 11-12) |
Table: Evidence summary for the identity, enzymology, localization, pathway function and phenotypes of Arabidopsis Q38933. Direct Arabidopsis findings are separated from comparative 2024 engineering evidence.
The identity is supported at two levels. First, an authoritative plant-carotenoid review explicitly lists At3g10230 as Arabidopsis β-carotene cyclase/βLCY1. Second, the Arabidopsis szl1 suppressor was genetically assigned to the LCYB structural gene and shown to encode a Gly-to-Glu substitution in a highly conserved region. The mutant enzyme retained reduced activity, establishing that szl1 is a hypomorphic allele of LCYB rather than an unrelated regulator. (li2009luteinaccumulationin pages 8-9, dellapenna2006vitaminsynthesisin pages 4-6)
No evidence retrieved suggested that the requested LCY1 symbol referred to a different Arabidopsis protein. Papers concerning carrot DcLCYB1, wolfberry LcLCYB, tomato CYC-B, or other species were treated only as comparative evidence and not as evidence of Q38933 identity.
LCYB catalyzes intramolecular cyclization of the linear C40 carotenoid all-trans-lycopene, creating β-ionone end rings. Its principal overall reaction can be summarized as:
all-trans-lycopene → γ-carotene → β-carotene
The first turnover cyclizes one ψ-end of lycopene to produce monocyclic γ-carotene; cyclization of the remaining end produces β-carotene. When LCYE first introduces an ε-ring to produce δ-carotene, LCYB can introduce a β-ring at the other end, yielding α-carotene. Thus, LCYB contributes to both major cyclic-carotenoid branches, but two LCYB-mediated β-cyclizations uniquely generate β-carotene. (ruizsola2012carotenoidbiosynthesisin pages 8-9, moreno2013levelsoflycopene pages 1-2)
Heterologous expression in lycopene-accumulating Escherichia coli showed that the Arabidopsis szl1 LCYB allele still produced β-carotene, but less than wild-type LCYB. When mutant LCYB was coexpressed with wild-type LCYE, the α-carotene:β-carotene molar ratio was 4:1, demonstrating that reduced LCYB activity changes branch partitioning rather than abolishing all cyclization. (li2009luteinaccumulationin pages 8-9)
The best-supported physiological substrate is all-trans-lycopene. LCYB also acts on the remaining ψ-end of monocyclic intermediates such as γ-carotene and, in combination with LCYE, δ-carotene. However, the retrieved literature did not provide purified Q38933 kinetic constants, comparative Km values for lycopene versus monocyclic substrates, or a systematic alternative-substrate panel. Substrate specificity is therefore established strongly at the pathway/product level but not quantitatively at the purified-enzyme level.
Q38933 is synthesized in the cytosol as a nuclear-encoded chloroplast precursor and imported into plastids through its N-terminal transit peptide. Comparative plant LCYB proteins commonly possess transit peptides within approximately the first 50–100 residues. Arabidopsis pathway and proteomic evidence places LCYB with membrane-associated carotenoid enzymes in the chloroplast, with evidence favoring association with the plastid-envelope carotenoid machinery. (ruizsola2012carotenoidbiosynthesisin pages 8-9, moreno2013levelsoflycopene pages 1-2)
The most defensible annotation is therefore:
Plastid/chloroplast-localized, membrane-associated carotenoid-biosynthetic enzyme.
The literature retrieved does not resolve a permanent integral-membrane topology or provide a quantitative distribution between envelope, thylakoid, and soluble plastid fractions. “Chloroplastic” is strongly supported; a narrowly specified intraplastid location should be stated more cautiously.
LCYB acts at the first major branch point after lycopene formation:
Because Arabidopsis has one principal LCYB, changes in its activity alter flux through both branches. Partial loss of LCYB favors the α-carotene/lutein branch while reducing β-carotene-derived xanthophylls. (li2009luteinaccumulationin pages 2-4, ruizsola2012carotenoidbiosynthesisin pages 8-9)
Cyclic carotenoids are structural and photoprotective constituents of photosynthetic pigment–protein complexes. β-Carotene is particularly important in photosystem reaction centers, while xanthophylls participate in light harvesting, antioxidant defense, and nonphotochemical quenching. LCYB therefore affects photosynthesis primarily by controlling the availability and composition of these pigments, rather than functioning as a conventional signaling receptor.
The szl1 npq1 double mutant provided especially precise evidence. It accumulated nearly twice as much lutein as wild type and had an approximately 75% smaller xanthophyll-cycle pool. Despite lacking zeaxanthin because of the npq1 lesion, elevated lutein partially restored energy-dependent nonphotochemical quenching: after five minutes of illumination, estimated qE was 1.7 in wild type, 0.8 in npq1, and 1.4 in szl1 npq1. This shows that altered LCYB flux can replace part of zeaxanthin’s photoprotective function with lutein. (li2009luteinaccumulationin pages 2-4)
Spectroscopy further detected lutein radical-cation formation in the affected antenna complexes, with an approximately 5-ps rise, 50–60-ps decay, and reconstructed peak near 920 nm. These measurements link the metabolic phenotype to a physical mechanism of excitation-energy dissipation. (li2009luteinaccumulationin pages 8-9)
Through β-carotene and xanthophyll production, LCYB supplies precursors for carotenoid-derived compounds. These include ABA precursors and diverse apocarotenoids; carotenoid metabolism also interfaces with strigolactone biology. These are downstream consequences of substrate supply, not evidence that LCYB directly synthesizes hormones. The principal annotation should remain carotenoid cyclization and branch control. (stra2025lycopeneβcyclaseoverexpression pages 1-2)
The supplied domain assignments are consistent with plant lycopene β-cyclases:
Authoritative synthesis describes plant LCYB and LCYE as flavoproteins requiring reduced FAD, despite cyclization having no overall net redox change. FAD is therefore thought to facilitate catalysis—potentially through transient electron/proton management or stabilization of carbocationic intermediates—rather than serving as a stoichiometrically consumed oxidant. The detailed mechanism is still less firmly established than the reaction itself. (ruizsola2012carotenoidbiosynthesisin pages 8-9)
Important evidence gaps include the absence of a retrieved experimental Q38933 structure, purified-enzyme cofactor stoichiometry, direct FAD-binding constants, or residue-by-residue Arabidopsis mutagenesis. Domain-to-function assignments should consequently be described as family-supported rather than fully resolved specifically for Q38933.
No retrieved 2023–2024 paper directly re-characterized At3g10230/Q38933. The foundational Arabidopsis conclusions continue to rest principally on the 1996 biochemical work, the 2009 szl1 genetic/photophysiological study, and later authoritative pathway syntheses. This absence of a recent Q38933-specific paper should not be interpreted as uncertainty about its core function; rather, contemporary research has shifted toward regulation, metabolic engineering, stress tolerance, and crop orthologs.
A relevant May 2024 study expressed wolfberry LcLCYB in tobacco. LcLCYB overexpression increased β-carotene 3.15-fold and total carotenoids 2.24-fold, while transgenic plants under salt stress showed reduced H₂O₂ and malondialdehyde and increased antioxidant-enzyme activities. These results demonstrate the current application potential of the LCYB enzyme class for biofortification and stress-resilient crops, but they are cross-species evidence and do not directly establish additional properties of Arabidopsis Q38933. (li2024carotenoidbiosynthesisgenes pages 1-2, li2024carotenoidbiosynthesisgenes pages 11-12)
The 2024 study also reported increased photosynthetic performance, proline, stress-responsive gene expression, and ABA after salinity treatment, supporting the view that manipulating carotenoid flux can have broader physiological effects. Such effects should be interpreted as downstream consequences of altered pigment and apocarotenoid metabolism, not necessarily as conserved direct molecular activities of every LCYB ortholog. (li2024carotenoidbiosynthesisgenes pages 1-2)
LCYB is an established target for:
Nevertheless, LCYB is not an isolated “more is always better” control point. Its effect depends on precursor supply, competition with LCYE, hydroxylation and cleavage downstream, plastid sink capacity, tissue context, and expression level. Comparative work shows that LCYB perturbation can alter chlorophyll, hormones, growth, and stress physiology; these pleiotropic outcomes require empirical testing in each crop. (moreno2013levelsoflycopene pages 1-2, stra2025lycopeneβcyclaseoverexpression pages 1-2, li2024carotenoidbiosynthesisgenes pages 11-12)
Recommended functional description:
Arabidopsis thaliana LCY1/LCYB/SZL1 (At3g10230; UniProt Q38933) is a nuclear-encoded, chloroplast-targeted, membrane-associated lycopene β-cyclase of the plant lycopene-cyclase flavoprotein family. It cyclizes β-end groups of all-trans-lycopene and monocyclic carotene intermediates, producing β-carotene through two β-cyclizations and contributing the β-ring of α-carotene in cooperation with LCYE. It controls partitioning between β,β-carotenoids and the β,ε/lutein branch, thereby determining the composition of photosynthetic and photoprotective carotenoids.
This annotation is supported strongly by locus assignment, Arabidopsis genetics, bacterial functional complementation, pigment profiling, and photophysiology. Chloroplast localization and reduced-FAD dependence are well supported at the pathway/family level, whereas exact intraplastid topology, purified-enzyme kinetics, alternative-substrate preferences, cofactor stoichiometry, and atomic structure remain incompletely characterized for Q38933 itself. (li2009luteinaccumulationin pages 8-9, li2009luteinaccumulationin pages 2-4, ruizsola2012carotenoidbiosynthesisin pages 8-9, dellapenna2006vitaminsynthesisin pages 4-6)
References
(li2009luteinaccumulationin pages 8-9): Zhirong Li, Tae Kyu Ahn, Thomas J. Avenson, Matteo Ballottari, Jeffrey A. Cruz, David M. Kramer, Roberto Bassi, Graham R. Fleming, Jay D. Keasling, and Krishna K. Niyogi. Lutein accumulation in the absence of zeaxanthin restores nonphotochemical quenching in the arabidopsis thaliana npq1 mutant. The Plant Cell, 21:1798-1812, Jun 2009. URL: https://doi.org/10.1105/tpc.109.066571, doi:10.1105/tpc.109.066571. This article has 256 citations.
(ruizsola2012carotenoidbiosynthesisin pages 8-9): M. Águila Ruiz-Sola and Manuel Rodríguez-Concepción. Carotenoid biosynthesis in arabidopsis: a colorful pathway. The Arabidopsis Book, 2012:e0158, Jan 2012. URL: https://doi.org/10.1199/tab.0158, doi:10.1199/tab.0158. This article has 742 citations and is from a peer-reviewed journal.
(dellapenna2006vitaminsynthesisin pages 4-6): Dean DellaPenna and Barry J. Pogson. Vitamin synthesis in plants: tocopherols and carotenoids. Jun 2006. URL: https://doi.org/10.1146/annurev.arplant.56.032604.144301, doi:10.1146/annurev.arplant.56.032604.144301. This article has 1126 citations and is from a domain leading peer-reviewed journal.
(moreno2013levelsoflycopene pages 1-2): Juan Camilo Moreno, Lorena Pizarro, Paulina Fuentes, Michael Handford, Victor Cifuentes, and Claudia Stange. Levels of lycopene β-cyclase 1 modulate carotenoid gene expression and accumulation in daucus carota. PLoS ONE, 8:e58144, Mar 2013. URL: https://doi.org/10.1371/journal.pone.0058144, doi:10.1371/journal.pone.0058144. This article has 123 citations and is from a peer-reviewed journal.
(li2009luteinaccumulationin pages 2-4): Zhirong Li, Tae Kyu Ahn, Thomas J. Avenson, Matteo Ballottari, Jeffrey A. Cruz, David M. Kramer, Roberto Bassi, Graham R. Fleming, Jay D. Keasling, and Krishna K. Niyogi. Lutein accumulation in the absence of zeaxanthin restores nonphotochemical quenching in the arabidopsis thaliana npq1 mutant. The Plant Cell, 21:1798-1812, Jun 2009. URL: https://doi.org/10.1105/tpc.109.066571, doi:10.1105/tpc.109.066571. This article has 256 citations.
(moreno2013levelsoflycopene pages 7-9): Juan Camilo Moreno, Lorena Pizarro, Paulina Fuentes, Michael Handford, Victor Cifuentes, and Claudia Stange. Levels of lycopene β-cyclase 1 modulate carotenoid gene expression and accumulation in daucus carota. PLoS ONE, 8:e58144, Mar 2013. URL: https://doi.org/10.1371/journal.pone.0058144, doi:10.1371/journal.pone.0058144. This article has 123 citations and is from a peer-reviewed journal.
(li2024carotenoidbiosynthesisgenes pages 1-2): Chen Li, Caili Wang, Zhiyang Cheng, Yu Li, and Wenjing Li. Carotenoid biosynthesis genes lclcyb, lclcye, and lcbch from wolfberry confer increased carotenoid content and improved salt tolerance in tobacco. Scientific Reports, May 2024. URL: https://doi.org/10.1038/s41598-024-60848-3, doi:10.1038/s41598-024-60848-3. This article has 21 citations and is from a peer-reviewed journal.
(li2024carotenoidbiosynthesisgenes pages 11-12): Chen Li, Caili Wang, Zhiyang Cheng, Yu Li, and Wenjing Li. Carotenoid biosynthesis genes lclcyb, lclcye, and lcbch from wolfberry confer increased carotenoid content and improved salt tolerance in tobacco. Scientific Reports, May 2024. URL: https://doi.org/10.1038/s41598-024-60848-3, doi:10.1038/s41598-024-60848-3. This article has 21 citations and is from a peer-reviewed journal.
(stra2025lycopeneβcyclaseoverexpression pages 1-2): Alice Stra, Juan C. Moreno, Jian You Wang, Ivan Petrik, Cristina Votta, Muhammad Jamil, Kit Xi Liew, Guan-Ting Erica Chen, Yagiz Alagoz, Claudia Stange, Valentina Fiorilli, Ondrej Novak, and Salim Al-Babili. Lycopene β-cyclase overexpression improves growth, modulates hormone content, and affects rhizospheric interactions in tobacco and tomato roots. Plant Cell Reports, Oct 2025. URL: https://doi.org/10.1007/s00299-025-03623-6, doi:10.1007/s00299-025-03623-6. This article has 2 citations and is from a peer-reviewed journal.