Recent Submissions

  • Light based underwater wireless communications

    Oubei, Hassan M.; Shen, Chao; Kammoun, Abla; Zedini, Emna; Park, Kihong; Sun, Xiaobin; Liu, Guangyu; Kang, Chun Hong; Ng, Tien Khee; Alouini, Mohamed-Slim; Ooi, Boon S. (IOP Science, 2018-07-17)
    Underwater wireless optical communication (UWOC) is a wireless communication technology that uses visible light to transmit data in underwater environment. Compared to radio-frequency (RF) and acoustic underwater techniques, UWOC has many advantages including large information bandwidth, unlicensed spectrum and low power requirements. This review paper provides an overview of the latest UWOC research. Additionally, we present a detailed description of transmitter and receiver technologies which are key components of UWOC systems. Moreover, studies investigating underwater optical channel models for both simple attenuation and the impact of turbulence including air bubbles and inhomogeneous salinity and temperature are also described. Future research challenges are identified and outlined.
  • Unleashing the potential of molecular beam epitaxy grown AlGaN-based ultraviolet-spectrum nanowires devices

    Min, Jungwook; Priante, Davide; Tangi, Malleswararao; Liu, Guangyu; Kang, Chun Hong; Prabaswara, Aditya; Zhao, Chao; Al-Maghrabi, Latifah; Alaskar, Yazeed; Albadri, Abdulrahman M.; Alyamani, Ahmed Y.; Ng, Tien Khee; Ooi, Boon S. (SPIE, 2018-07-12)
    There have been recent research advances in AlGaN-based self-assembled nanowires (NWs) as building blocks for ultraviolet (UV) optoelectronics grown by plasma-assisted molecular beam epitaxy. We review the basic growth kinetics on various foundry-compatible-metal/silicon-based substrates and the epistructure design for UV devices. We highlight the use of diffusion-barrier-metal thin film on silicon substrate as a solution to enhance device performance. NWs offer the opportunity to mitigate the detrimental quantum-confined Stark effect (QCSE), which lowers the recombination rate thereby reducing the device efficiency. On the other hand, the polarization-induced doping from the graded composition along NWs can be advantageous for eluding the inefficient doping in AlGaN-based UV devices. Sidewall surface states and the associate passivation treatment, as well as the use of ultrafast electron-microscopy characterization, are crucial investigations in shedding light on device performance under the influence of surface dangling bonds. For investigating the electrical performance of individual NWs and NWs light-emitting diode as a single entity, recent reports based on conductive atomic force microscopy measurements provide fast-prototyping in-process pass-fail evaluation and a means of improving growth for high-performance devices. Stress tests of NWs devices, crucial for reliable operation, are also discussed. Beyond applications in LEDs, an AlGaN-based NWs solar-blind photodetector demonstrated leveraging on the dislocation-free active region, reduced QCSE, enhanced light absorption, and tunable-composition features. The review opens pathways and offers insights for practical realization of AlGaN-based axial NWs devices on scalable and low-cost silicon substrates.
  • Diode junction temperature in ultraviolet AlGaN quantum-disks-in-nanowires

    Priante, Davide; Elafandy, Rami T.; Prabaswara, Aditya; Janjua, Bilal; Zhao, Chao; Alias, Mohd Sharizal; Tangi, Malleswararao; Alaskar, Yazeed; Albadri, Abdulrahman M.; Alyamani, Ahmed Y.; Ng, Tien Khee; Ooi, Boon S. (AIP, 2018-07-05)
    The diode junction temperature (Tj) of light emitting devices is a key parameter affecting the efficiency, output power, and reliability. Herein, we present experimental measurements of the Tj on ultraviolet (UV) AlGaN nanowire (NW) light emitting diodes (LEDs), grown on a thin metal-film and silicon substrate using the diode forward voltage and electroluminescence peak-shift methods. The forward-voltage vs temperature curves show temperature coefficient dVF/dT values of −6.3 mV/°C and −5.2 mV/°C, respectively. The significantly smaller Tj of ∼61 °C is measured for the sample on the metal substrate, as compared to that of the sample on silicon (∼105 °C), at 50 mA, which results from the better electrical-to-optical energy conversion and the absence of the thermally insulating SiNx at the NWs/silicon interface. In contrast to the reported higher Tj values for AlGaN planar LEDs exhibiting low lateral and vertical heat dissipation, we obtained a relatively lower Tj at similar values of injection current. Lower temperatures are also achieved using an Infrared camera, confirming that the Tj reaches higher values than the overall device temperature. Furthermore, the heat source density is simulated and compared to experimental data. This work provides insight into addressing the high junction temperature limitations in light-emitters, by using a highly conductive thin metal substrate, and it aims to realize UV AlGaN NWs for high power and reliable emitting devices.
  • Review of nanophotonics approaches using nanostructures and nanofabrication for III-nitrides ultraviolet-photonic devices

    Alias, Mohd Sharizal; Tangi, Malleswararao; Holguin Lerma, Jorge Alberto; Stegenburgs, Edgars; Alatawi, Abdullah; Ashry, Islam; Subedi, Ram Chandra; Priante, Davide; Shakfa, Mohammad Khaled; Ng, Tien Khee; Ooi, Boon S. (SPIE, 2018-07-05)
    Group III-nitride semiconductor materials especially AlGaN are key-emerging candidates for the advancement of ultraviolet (UV) photonic devices. Numerous nanophotonics approaches using nanostructures (e.g., nanowires, nanorods, and quantum dots/disks) and nanofabrication (e.g., substrate patterning, photonic crystals, nanogratings, and surface-plasmons) have been demonstrated to address the material growth challenges and to enhance the device efficiencies of photonic devices operating at UV wavelengths. Here, we review the progress of nanophotonics implementations using nanostructured interfaces and nanofabrication approaches for the group III-nitride semiconductors to realize efficient UV-based photonic devices. The existing challenges of nanophotonics applications are presented. This review aims to provide analysis of state-of-the-art nanophotonic approaches in advancing the UV-photonic devices based on group III-nitride semiconductors.
  • Supplementary Material for: Observations and cloud-resolving modeling of haboob dust storms over the Arabian Peninsula

    Anisimov, Anatolii; Axisa, Duncan; Kucera, Paul A.; Mostamandi, Suleiman; Stenchikov, Georgiy L. (2018-06-28)
  • Investigation of Self-injection Locked Visible Laser Diodes for High Bit-rate Visible Light Communication

    Shamim, Md. Hosne Mobarok; Shemis, Mohamed; Shen, Chao; Oubei, Hassan M.; Ng, Tien Khee; Ooi, Boon S.; Khan, Mohammed Zahed Mustafa (IEEE, 2018-06-22)
    We report on self-injection locking in InGaN/GaN (blue/green) and InGaP/AlGaInP (red) visible-light laser diodes. The free-space optical feedback path was accomplished via an external mirror. The effect of injection current, optical power injection ratio, and external cavity length on the spectral linewidth and modulation bandwidth of the lasers are investigated. Our results show that the laser performance was substantially improved. In particular, we achieved a significant increase of ~57% (1.53 GHz - 2.41 GHz) and ~ 31 % (1.72 GHz - 2.26 GHz) in the modulation bandwidth, and ~9 (1.0 nm to 0.11 nm) and ~ 9 (0.63 nm to 0.07nm) times reduction in spectral linewidth of the green and blue lasers, respectively. Consequently, side-mode-suppression-ratio was considerably increased in all the cases, reaching as high as ~20 dB in self-injection locked blue laser diode, thus enabling a close to single mode operation. This work paves the way for attaining high speed optical wireless communications by overcoming the challenges of limited modulation bandwidth and multimode operation of visible laser diodes with this simple scheme.
  • Ignition delay time sensitivity in ignition quality tester (IQT) and its relation to octane sensitivity

    Naser, Nimal; Sarathy, Mani; Chung, Suk-Ho (Elsevier, 2018-06-22)
    Cetane number (CN) is a commonly used metric to rate the ignition quality of distillate fuels. In this work, a concept of sensitivity in ignition delay time (IDT) obtained with an ignition quality tester (IQT) is proposed, which is correlated to octane sensitivity (OS), i.e., the difference between research octane number (RON) and motor octane number (MON). The concept is based on the determination of IDT using the ASTM D6890 standard and IDT obtained at a temperature lower than that prescribed by the standard. The IDT measured at this lower temperature is referred to as IDT_l , which is obtained via a calibration procedure similar to the ASTM D6890 standard, but with a higher value of reference IDT for calibration with n-heptane. The IDT_h (measured at the derived cetane number (DCN) ASTM D6890 condition) of a given test fuel and a binary primary reference fuel (PRF) mixture of iso- octane and n-heptane was measured to identify a PRF with matching IDT_h as the test fuel. The ratio of low temperature IDTs of the non-PRF test fuel and PRF, i.e., IDT_l,non-PRF/IDT_l,PRF was defined as IDT sensitivity (IDS), which was correlated with the OS of the test fuel. The RON and MON values of a wide range of fuel classes including surrogate fuels and fully blended practical fuels were estimated, and showed satisfactory agreement with measured RON/MON values. The RON values of many pure components that could not be measured with standard test methods were also estimated. Two certification diesels and Saudi Arabian pump grade diesel were also tested.
  • Constructing robust and highly-selective hydrogel membranes by bioadhesion-inspired method for CO 2 separation

    Wu, Yingzhen; Zhou, Tiantian; Wu, Hong; Fu, Weixian; Wang, Xinru; Wang, Shaofei; Yang, Leixin; Wu, Xingyu; Ren, Yanxiong; Jiang, Zhongyi; Wang, Baoyi (Elsevier BV, 2018-06-01)
    Water-swollen hydrogel membranes are good candidates for CO2 separations due to the favorable solubility of CO2 in water. However, the excessive amount of water often causes the poor mechanical property and low selectivity. Herein, we propose a bioadhesion-inspired method to construct robust and high-performance CO2 separation membranes via in situ generation of polydopamine (PDA) nanoaggregates within poly (vinyl alcohol) (PVA) matrix. PDA nanoaggregates entangled with PVA chains and formed hydrogen bonding with hydroxyl groups from PVA chains. Physical cross-linking occurred between PVA chains and PDA nanoaggregates. Compared with the PVA membrane, the PVA-PDA hybrid membrane with the dopamine content of 0.5mol% exhibited a 1.7-fold increase in tensile strength and a 2.2-fold increase in the tensile modulus. The membranes were used for CO2/CH4 separation. The physical cross-linking resulted in a PVA chain rigidification region around PDA nanoaggregates, which hindered the penetration of larger-size gas molecules and thus enhancing the CO2/CH4 selectivity. Moreover, the abundant amine groups from PDA nanoaggregates could facilitate CO2 transport. The optimized hybrid hydrogel membrane exhibited CO2/CH4 selectivity of 43.2, which was 43.85% higher than that of the PVA membrane. The bioadhesion-inspired method opens up new opportunities to exploit the potential application of hydrogel membranes.
  • Species delineation and hybrid identification using diagnostic nuclear markers for Plectropomus leopardus and Plectropomus maculatus

    He, Song; Harrison, Hugo B.; Berumen, Michael L. (Elsevier BV, 2018-06-01)
    Diagnostic molecular markers are an essential tool in the study of species’ ecology and evolution, particularly in closely related and sympatric species. Furthermore, the increasing awareness of wild-hybrids has led to a renewed interest in rapid diagnostic assays. Here, we test the ability of two mitochondrial (Cytb and COI) and two nuclear markers (ETS2 and TMO-4c4) to confidently discriminate purebred P. leopardus and P. maculatus and their first-generation hybrids. A sample of 48 purebred individuals and 91 interspecific hybrids were used in this study and their delineation confirmed using a set of microsatellite markers. Our results indicate mitochondrial markers could not distinguish even between species but both nuclear markers confidently identified species and first-generation hybrids. However, later-generation hybrids could not always be confidently identified due to on-going introgression between species. Our findings provide a robust tool to distinguish purebred individuals and interspecific hybrids in a pair of species with an unexpectedly high incidence of hybridization. The quick species discrimination abilities provided by these diagnostic markers are important for stock assessment and recruitment studies of these important fishery species.
  • Bacterial polyextremotolerant bioemulsifiers from arid soils improve water retention capacity and humidity uptake in sandy soil

    Raddadi, Noura; Giacomucci, Lucia; Marasco, Ramona; Daffonchio, Daniele; Cherif, Ameur; Fava, Fabio (Springer Nature, 2018-05-31)
    Water stress is a critical issue for plant growth in arid sandy soils. Here, we aimed to select bacteria producing polyextremotolerant surface-active compounds capable of improving water retention and humidity uptake in sandy soils.From Tunisian desert and saline systems, we selected eleven isolates able to highly emulsify different organic solvents. The bioemulsifying activities were stable with 30% NaCl, at 4 and 120 °C and in a pH range 4-12. Applications to a sandy soil of the partially purified surface-active compounds improved soil water retention up to 314.3% compared to untreated soil. Similarly, after 36 h of incubation, the humidity uptake rate of treated sandy soil was up to 607.7% higher than untreated controls.Overall, results revealed that polyextremotolerant bioemulsifiers of bacteria from arid and desert soils represent potential sources to develop new natural soil-wetting agents for improving water retention in arid soils.
  • The Arabidopsis homolog of human G3BP1 is a key regulator of stomatal and apoplastic immunity

    Abulfaraj, Aala A.; Mariappan, Kiruthiga; Bigeard, Jean; Manickam, Prabhu; Blilou, Ikram; Guo, Xiujie; Al-Babili, Salim; Pflieger, Delphine; Hirt, Heribert; Rayapuram, Naganand (Life Science Alliance, LLC, 2018-05-31)
    Mammalian Ras-GTPase–activating protein SH3-domain–binding proteins (G3BPs) are a highly conserved family of RNA-binding proteins that link kinase receptor-mediated signaling to RNA metabolism. Mammalian G3BP1 is a multifunctional protein that functions in viral immunity. Here, we show that the Arabidopsis thaliana homolog of human G3BP1 negatively regulates plant immunity. Arabidopsis g3bp1 mutants showed enhanced resistance to the virulent bacterial pathogen Pseudomonas syringae pv. tomato. Pathogen resistance was mediated in Atg3bp1 mutants by altered stomatal and apoplastic immunity. Atg3bp1 mutants restricted pathogen entry into stomates showing insensitivity to bacterial coronatine–mediated stomatal reopening. AtG3BP1 was identified as a negative regulator of defense responses, which correlated with moderate up-regulation of salicylic acid biosynthesis and signaling without growth penalty.
  • Towards informed metrics for examining the role of human-induced animal responses in tag studies on wild animals

    Wilson, Rory P.; Holton, Mark; Wilson, Vianney L.; Gunner, Richard; Tysse, Brenda; Wilson, Gwendoline I; Quintana, Flavio; Duarte, Carlos M.; Scantlebury, D. Michael (Wiley, 2018-05-31)
    Two prime issues can detrimentally affect animals that have been equipped with tags; (i) the effect of the capture and restraint process and (ii) the effect of the tag itself. This work examines some of the issues surrounding quantification of tag effects on wild animals for both restrained and free-living animals. A new method to quantify stress effects based on monitoring ventilation rates in relation to activity is suggested for restrained animals which may help improve the practice of handling animals. It is also suggested that various metrics, many derived from accelerometers, can be examined in tagged wild animals to examine the change in behaviours over time with a view to having a better understanding of welfare issues, assuring the quality of recorded data and informing best practice. This article is protected by copyright. All rights reserved.
  • Hydrothermal synthesis of p-type nanocrystalline NiO nanoplates for high response and low concentration hydrogen gas sensor application

    Nakate, Umesh T.; Lee, Gun Hee; Ahmad, Rafiq; Patil, Pramila; Bhopate, Dhanaji P.; Hahn, Y.B.; Yu, Y.T.; Suh, Eun-kyung (Elsevier BV, 2018-05-30)
    High quality nanocrystalline NiO nanoplates were synthesized using surfactant and template free hydrothermal route. The gas sensing properties of NiO nanoplates were investigated. The nanoplates morphology of NiO with average thickness ~20 nm and diameter ~100 nm has been confirmed by FE-SEM and TEM. Crystalline quality of NiO has been studied using HRTEM and SAED techniques. Structural properties and elemental compositions have been analysed by XRD and energy dispersive spectrometer (EDS) respectively. The detailed investigation of structural parameters has been carried out. The optical properties of NiO were analyzed from UV-Visible and photoluminescence spectra. NiO nanoplates have good selectivity towards hydrogen (H2) gas. The lowest H2 response of 3% was observed at 2 ppm, whereas 90% response was noted for 100 ppm at optimized temperature of 200 °C with response time 180 s. The H2 responses as functions of different operating temperature as well as gas concentrations have been studied along with sensor stability. The hydrogen sensing mechanism was also elucidated.
  • Carrier dynamics of InxGa1-xN/GaN multiple quantum wells grown on (−201) β-Ga2O3 for bright vertical light emitting diodes

    Mumthaz Muhammed, Mufasila; Xu, Jian; Wehbe, Nimer; Roqan, Iman S. (The Optical Society, 2018-05-30)
    High-quality InxGa1-xN/GaN multi-quantum well (MQW) structures (0.05≤x≤0.13), are successfully grown on transparent and conductive (−201)-oriented β-Ga2O3 substrate. Scanning-transmission electron microscopy and secondary ion mass spectrometry (SIMS) show well-defined high quality MQWs, while the In and Ga compositions in the wells and the barriers are estimated by SIMS. Temperature-dependant Photoluminescence (PL) confirms high optical quality with a strong bandedge emission and negligble yellow band. time-resolved PL measurements (via above/below-GaN bandgap excitations) explain carrier dynamics, showing that the radiative recombination is predominant. Our results demonstrate that (−201)-oriented β-Ga2O3 is a strong candidate as a substrate for III-nitride-based vertical- emitting devices.
  • Flexible InGaN nanowire membranes for enhanced solar water splitting

    Elafandy, Rami T.; Elafandy, Rami T.; Min, Jung-Wook; Zhao, Chao; Ng, Tien Khee; Ooi, Boon S. (The Optical Society, 2018-05-30)
    III-Nitride nanowires (NWs) have recently emerged as potential photoelectrodes for efficient solar hydrogen generation. While InGaN NWs epitaxy over silicon is required for high crystalline quality and economic production, it leads to the formation of the notorious silicon nitride insulating interface as well as low electrical conductivity which both impede excess charge carrier dynamics and overall device performance. We tackle this issue by developing, for the first time, a substrate-free InGaN NWs membrane photoanodes, through liftoff and transfer techniques, where excess charge carriers are efficiently extracted from the InGaN NWs through a proper ohmic contact formed with a high electrical conductivity metal stack membrane. As a result, compared to conventional InGaN NWs on silicon, the fabricated free-standing flexible membranes showed a 10-fold increase in the generated photocurrent as well as a 0.8 V cathodic shift in the onset potential. Through electrochemical impedance spectroscopy, accompanied with TEM-based analysis, we further demonstrated the detailed enhancement within excess charge carrier dynamics of the photoanode membranes. This novel configuration in photoelectrodes demonstrates a novel pathway for enhancing the performance of III-nitrides photoelectrodes to accelerate their commercialization for solar water splitting.
  • Chick chorioallantoic membrane assay as an in vivo model to study the effect of nanoparticle-based anticancer drugs in ovarian cancer

    Vu, Binh Thanh; Shahin, Sophia Allaf; Croissant, Jonas G.; Fatieiev, Yevhen; Matsumoto, Kotaro; Le-Hoang Doan, Tan; Yik, Tammy; Simargi, Shirleen; Conteras, Altagracia; Ratliff, Laura; Jimenez, Chiara Mauriello; Raehm, Laurence; Khashab, Niveen M.; Durand, Jean-Olivier; Glackin, Carlotta; Tamanoi, Fuyuhiko (Springer Nature, 2018-05-29)
    New therapy development is critically needed for ovarian cancer. We used the chicken egg CAM assay to evaluate efficacy of anticancer drug delivery using recently developed biodegradable PMO (periodic mesoporous organosilica) nanoparticles. Human ovarian cancer cells were transplanted onto the CAM membrane of fertilized eggs, resulting in rapid tumor formation. The tumor closely resembles cancer patient tumor and contains extracellular matrix as well as stromal cells and extensive vasculature. PMO nanoparticles loaded with doxorubicin were injected intravenously into the chicken egg resulting in elimination of the tumor. No significant damage to various organs in the chicken embryo occurred. In contrast, injection of free doxorubicin caused widespread organ damage, even when less amount was administered. The lack of toxic effect of nanoparticle loaded doxorubicin was associated with specific delivery of doxorubicin to the tumor. Furthermore, we observed excellent tumor accumulation of the nanoparticles. Lastly, a tumor could be established in the egg using tumor samples from ovarian cancer patients and that our nanoparticles were effective in eliminating the tumor. These results point to the remarkable efficacy of our nanoparticle based drug delivery system and suggests the value of the chicken egg tumor model for testing novel therapies for ovarian cancer.
  • Quantified Hole Concentration in AlGaN Nanowires for High-Performance Ultraviolet Emitters

    Zhao, Chao; Ebaid, Mohamed; Zhang, Huafan; Priante, Davide; Janjua, Bilal; Zhang, Daliang; Wei, Nini; Alhamoud, Abdullah; Shakfa, M. Khaled; Ng, Tien Khee; Ooi, Boon S. (Royal Society of Chemistry (RSC), 2018-05-29)
    P-type doping in wide bandgap and new classes of ultra-wide bandgap materials has long been a scientific and engineering problem. The challenges arise from the large activation energy of dopants and high densities of dislocations in materials. We report here, a significantly enhanced p-type conduction using high-quality AlGaN nanowires. For the first time, the hole concentration in Mg-doped AlGaN nanowires is quantified. The incorporation of Mg into AlGaN was verified by correlation with photoluminescence and Raman measurements. The open-circuit potential measurements further confirmed the p-type conductivity; while Mott-Schottky experiments measured a hole concentration of 1.3×1019 cm-3. These results from photoelectrochemical measurements allow us to design prototype ultraviolet (UV) light-emitting diodes (LEDs) incorporating the AlGaN quantum-disks-in-nanowire and optimized p-type AlGaN contact layer for UV-transparency. The ~335-nm LEDs exhibited a low turn-on voltage of 5 V with a series resistance of 32 Ω, due to the efficient p-type doping of the AlGaN nanowires. The bias-dependent Raman measurements further revealed the negligible self-heating of devices. This study provides an attractive solution to evaluate electrical properties of AlGaN, which is applicable to other wide bandgap nanostructures. Our results are expected to open doors to new applications for wide and ultra-wide bandgap materials.
  • Genetic Determinants Associated With in Vivo Survival of Burkholderia cenocepacia in the Caenorhabditis elegans Model

    Wong, Yee-Chin; Abd El Ghany, Moataz; Ghazzali, Raeece N. M.; Yap, Soon-Joo; Hoh, Chee-Choong; Pain, Arnab; Nathan, Sheila (Frontiers Media SA, 2018-05-29)
    A Burkholderia cenocepacia infection usually leads to reduced survival and fatal cepacia syndrome in cystic fibrosis patients. The identification of B. cenocepacia essential genes for in vivo survival is key to designing new anti-infectives therapies. We used the Transposon-Directed Insertion Sequencing (TraDIS) approach to identify genes required for B. cenocepacia survival in the model infection host, Caenorhabditis elegans. A B. cenocepacia J2315 transposon pool of ∼500,000 mutants was used to infect C. elegans. We identified 178 genes as crucial for B. cenocepacia survival in the infected nematode. The majority of these genes code for proteins of unknown function, many of which are encoded by the genomic island BcenGI13, while other gene products are involved in nutrient acquisition, general stress responses and LPS O-antigen biosynthesis. Deletion of the glycosyltransferase gene wbxB and a histone-like nucleoid structuring (H-NS) protein-encoding gene (BCAL0154) reduced bacterial accumulation and attenuated virulence in C. elegans. Further analysis using quantitative RT-PCR indicated that BCAL0154 modulates B. cenocepacia pathogenesis via transcriptional regulation of motility-associated genes including fliC, fliG, flhD, and cheB1. This screen has successfully identified genes required for B. cenocepacia survival within the host-associated environment, many of which are potential targets for developing new antimicrobials.
  • Candidate enzymes for saffron crocin biosynthesis are localized in multiple cellular compartments

    Demurtas, Olivia Costantina; Frusciante, Sarah; Ferrante, Paola; Diretto, Gianfranco; Azad, Noraddin Hosseinpour; Pietrella, Marco; Aprea, Giuseppe; Taddei, Anna Rita; Romano, Elena; Mi, Jianing; Al-Babili, Salim; Frigerio, Lorenzo; Giuliano, Giovanni (American Society of Plant Biologists (ASPB), 2018-05-29)
    Saffron is composed of the dried stigmas of Crocus sativus and is the most expensive spice on Earth. Its red color is due to the apocarotenoid glycosides, crocins, which accumulate in the vacuole and reach up to 10% of the stigma dry weight. We have previously characterized the first dedicated enzyme in crocin biosynthesis, CsCCD2, which cleaves zeaxanthin to yield crocetin dialdehyde. In this work, we identified six putative aldehyde dehydrogenase (ALDH) transcripts expressed in saffron stigmas. When expressed in E. coli, only one of corresponding proteins (CsALDH3I1), was able to convert crocetin dialdehyde into the crocin precursor, crocetin. CsALDH3I1 carries a C-terminal hydrophobic domain, similar to that of a Neurospora membrane-associated apocarotenoid dehydrogenase, YLO-1. We also characterized a UDP-glycosyltransferase enzyme, CsUGT74AD1, able to convert crocetin to crocins 1 and 2'. In vitro assays showed high specificity of CsALDH3I1 for crocetin dialdehyde and long chain apocarotenals, and of CsUGT74AD1 for crocetin. Upon extract fractionation, the CsCCD2, CsALDH3I1 and CsUGT74AD1 enzymes partitioned in the insoluble fraction, suggesting that they are associated to membranes or to large insoluble complexes. Immunogold labeling of saffron stigmas and confocal microscopy of fusions to Green Fluorescent Protein expressed in N. benthamiana leaves revealed that CsCCD2 localizes to plastids, CsALDH3I1 to the endoplasmic reticulum (ER) and CsUGT74AD1 to the cytoplasm, in association with cytoskeletal-like structures. Based on our and on literature data, we propose that the ER and cytoplasm function as

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