Polyploidy underlies co-option and diversification of biosynthetic triterpene pathways in the apple tribe.

Whole-genome duplication (WGD) plays important roles in plant evolution and function, yet little is known about how WGD underlies metabolic diversification of natural products that bear significant medicinal properties, especially in nonmodel trees. Here, we reveal how WGD laid the foundation for co-option and differentiation of medicinally important ursane triterpene pathway duplicates, generating distinct chemotypes between species and between developmental stages in the apple tribe. After generating chromosome-level assemblies of a widely cultivated loquat variety and Gillenia trifoliata, we define differentially evolved, duplicated gene pathways and date the WGD in the apple tribe at 13.5 to 27.1 Mya, much more recent than previously thought. We then functionally characterize contrasting metabolic pathways responsible for major triterpene biosynthesis in G. trifoliata and loquat, which pre- and postdate the Maleae WGD, respectively. Our work mechanistically details the metabolic diversity that arose post-WGD and provides insights into the genomic basis of medicinal properties of loquat, which has been used in both traditional and modern medicines.

Betalain biosynthesis in red pulp pitaya is regulated via HuMYB132: a R-R type MYB transcription factor.

BACKGROUND: Multiple MYB transcription factors (TFs) are involved in the regulation of plant coloring. Betalain is a kind of natural plant pigment and its biosynthesis is regulated by a number of enzymes. Despite this, little is known about the molecular properties and roles of MYB TFs in pitaya betalain biosynthesis. RESULTS: In the present study, we identified a 1R-MYB gene, HuMYB132, which is preferentially expressed in red-pulp pitaya at the mature stage. It was clustered with Arabidopsis R-R-type genes and had two DNA-binding domains and a histidine-rich region. The expression assays in N. benthamiana and yeast indicated that HuMYB132 is a nucleus-localized protein with transcriptional activation activity. Dual luciferase reporter assay and electrophoretic mobility shift assays (EMSA) demonstrated that HuMYB132 could promote the transcriptional activities of HuADH1, HuCYP76AD1-1, and HuDODA1 by binding to their promoters. Silencing HuMYB132 reduced betalain accumulation and the expression levels of betalain biosynthetic genes in pitaya pulps. CONCLUSIONS: According to our findings, HuMYB132, a R-R type member of 1R-MYB TF subfamily, positively regulates pitaya betalain biosynthesis by regulating the expression of HuADH1, HuCYP76AD1-1, and HuDODA1. The present study provides a new theoretical reference for the management of pitaya betalain biosynthesis and also provides an essential basis for future regulation of betalain biosynthesis in Hylocereus.

Massively parallel FMCW lidar with cm range resolution using an electro-optic frequency comb.

Frequency-modulated continuous wave (FMCW) light detection and ranging (lidar) is a promising solution for three-dimensional (3D) imaging and autonomous driving. This technique maps range and velocity measurement to frequency counting via coherent detection. Compared with single-channel FMCW lidar, multi-channel FMCW lidar can greatly improve the measurement rate. A chip-scale soliton micro-comb is currently used in FMCW lidar to enable multi-channel parallel ranging and significantly increase the measurement rate. However, its range resolution is limited due to the soliton comb having only a few-GHz frequency sweep bandwidth. To overcome this limitation, we propose using a cascaded modulator electro-optic (EO) frequency comb for massively parallel FMCW lidar. We demonstrate a 31-channel FMCW lidar with a bulk EO frequency comb and a 19-channel FMCW lidar using an integrated thin-film lithium niobate (TFLN) EO frequency comb. Both systems have a sweep bandwidth of up to 15 GHz for each channel, corresponding to a 1-cm range resolution. We also analyze the limiting factors of the sweep bandwidth in 3D imaging and perform 3D imaging for a specific target. The measurement rate achieved is over 12 megapixels per second, which verifies its feasibility for massively parallel ranging. Our approach has the potential to greatly benefit 3D imaging in fields where high range resolution is required, such as in criminal investigation and precision machining.

Identification of HuSPL family and key role of HuSPL12 in regulation of betalain biosynthesis in pitaya.

The SQUAMOSA promoter binding protein-like (SPL) gene family is a unique family of plant-specific transcription factors (TFs), which plays vital roles in a variety of plant biological processes. Its role in betalain biosynthesis in Hylocereus undantus; however, is still unclear. Here, we report a total of 16 HuSPL genes from the pitaya genome, which were unevenly distributed among nine chromosomes. The HuSPL genes were clustered into seven groups, and most HuSPLs within the same group shared similar exon-intron structures and conserved motifs. Eight segment replication events in the HuSPL gene family were the main driving force behind the gene family expansion. Nine of the HuSPL genes had potential target sites for Hmo-miR156/157b. Hmo-miR156/157b-targeted HuSPLs exhibited differential expression patterns compared with constitutive expression patterns of most Hmo-miR156/157b-nontargeted HuSPLs. The expression of Hmo-miR156/157b gradually increased during fruit maturation, while the expression of Hmo-miR156/157b-targeted HuSPL5/11/14 gradually decreased. In addition, the lowest expression level of Hmo-miR156/157b-targeted HuSPL12 was detected 23rd day after flowering, when the middle pulps started to turn red. HuSPL5, HuSPL11, HuSPL12, and HuSPL14 were nucleus-localized proteins. HuSPL12 could inhibit the expression of HuWRKY40 by binding to its promoter. Results from yeast two-hybrid and bimolecular fluorescence complementation assays showed that HuSPL12 could interact with HuMYB1, HuMYB132, or HuWRKY42 TFs responsible for betalain biosynthesis. The results of the present study provide an essential basis for future regulation of betalain accumulation in pitaya.

Identification of HuSWEET Family in Pitaya (Hylocereus undatus) and Key Roles of HuSWEET12a and HuSWEET13d in Sugar Accumulation.

The sugar composition and content of fruit have a significant impact on their flavor and taste. In pitaya, or dragon fruit, sweetness is a crucial determinant of fruit taste and consumer preference. The sugars will eventually be exported transporters (SWEETs), a novel group of sugar transporters that have various physiological functions, including phloem loading, seed filling, nectar secretion, and fruit development. However, the role of SWEETs in sugar accumulation in pitaya fruit is not yet clear. Here, we identified 19 potential members (HuSWEET genes) of the SWEET family in pitaya and analyzed their conserved motifs, physiochemical characteristics, chromosomal distribution, gene structure, and phylogenetic relationship. Seven highly conserved α-helical transmembrane domains (7-TMs) were found, and the HuSWEET proteins can be divided into three clades based on the phylogenetic analysis. Interestingly, we found two HuSWEET genes, HuSWEET12a and HuSWEET13d, that showed strong preferential expressions in fruits and an upward trend during fruit maturation, suggesting they have key roles in sugar accumulation in pitaya. This can be further roughly demonstrated by the fact that transgenic tomato plants overexpressing HuSWEET12a/13d accumulated high levels of sugar in the mature fruit. Together, our result provides new insights into the regulation of sugar accumulation by SWEET family genes in pitaya fruit, which also set a crucial basis for the further functional study of the HuSWEETs.

An Imidazole-Based Triangular Macrocycle for Visual Detection of Formaldehyde.

Highly selective detection of formaldehyde utilizing supramolecules has promising applications in both environmental monitoring and biomonitoring areas. Herein we present a new class of imidazole-based, coordination-driven, self-assembled triangular macrocycles with specific recognition of formaldehyde. The visible fluorescence change to the naked eye from yellow to green-yellow occurs via an unusual reversible hydroxymethylation reaction of imidazole, whereas the corresponding imidazole ligands show no fluorescence change. This study provides a new method for efficient formaldehyde detection by utilizing imidazole-based coordination supramolecules.

HuNAC20 and HuNAC25, Two Novel NAC Genes from Pitaya, Confer Cold Tolerance in Transgenic Arabidopsis.

NAC transcription factors are one of the largest families of transcriptional regulators in plants, and members of the gene family play vital roles in regulating plant growth and development processes including biotic/abiotic stress responses. However, little information is available about the NAC family in pitaya. In this study, we conducted a genome-wide analysis and a total of 64 NACs (named HuNAC1-HuNAC64) were identified in pitaya (Hylocereus). These genes were grouped into fifteen subgroups with diversities in gene proportions, exon-intron structures, and conserved motifs. Genome mapping analysis revealed that HuNAC genes were unevenly scattered on all eleven chromosomes. Synteny analysis indicated that the segmental duplication events played key roles in the expansion of the pitaya NAC gene family. Expression levels of these HuNAC genes were analyzed under cold treatments using qRT-PCR. Four HuNAC genes, i.e., HuNAC7, HuNAC20, HuNAC25, and HuNAC30, were highly induced by cold stress. HuNAC7, HuNAC20, HuNAC25, and HuNAC30 were localized exclusively in the nucleus. HuNAC20, HuNAC25, and HuNAC30 were transcriptional activators while HuNAC7 was a transcriptional repressor. Overexpression of HuNAC20 and HuNAC25 in Arabidopsis thaliana significantly enhanced tolerance to cold stress through decreasing ion leakage, malondialdehyde (MDA), and H2O2 and O2- accumulation, accompanied by upregulating the expression of cold-responsive genes (AtRD29A, AtCOR15A, AtCOR47, and AtKIN1). This study presents comprehensive information on the understanding of the NAC gene family and provides candidate genes to breed new pitaya cultivars with tolerance to cold conditions through genetic transformation.

Genome-Wide Identification of WRKY Gene Family in Pitaya Reveals the Involvement of HmoWRKY42 in Betalain Biosynthesis.

The WRKY gene family is a plant-specific transcription factor (TF) that regulates many physiological processes and (a) biotic stress responses. Despite this, little is known about the molecular properties and roles of WRKY TFs in pitaya betalain biosynthesis. Here we report the identification of 70 WRKY in Hylocereus undatus, their gene structure, locations on each chromosome, systematic phylogenetic analysis, conserved motif analysis, and synteny of HuWRKY genes. HmoWRKY42 is a Group IIb WRKY protein and contains a coiled-coil motif, a WRKY domain and a C2H2 zinc-finger motif (CX5CX23HXH). Results from yeast one-hybrid and transient dual-luciferase assays showed that HmoWRKY42 was a transcriptional repressor and could repress HmocDOPA5GT1 expression by binding to its promoter. Yeast two-hybrid assays showed that HmoWRKY42 could interact with itself to form homodimers. Knocking out the coiled-coil motif of HmoWRKY42 prevented its self-interaction and prevented it from binding to the HmocDOPA5GT1 promoter. Knocking out the WRKY domain and C2H2 zinc-finger motif sequence of HmoWRKY42 also prevented it from binding to the HmocDOPA5GT1 promoter. The coiled-coil motif, the WRKY domain and the C2H2 zinc finger motif are key motifs for the binding of HmoWRKY42 to the HmocDOPA5GT1 promoter. HmoWRKY42 is localized in the nucleus and possesses trans-activation ability responsible for pitaya betalain biosynthesis by repressing the transcription of HmocDOPA5GT1. As far as we know, no reports are available on the role of HmoWRKY42 in pitaya betalain biosynthesis. The results provide an important foundation for future analyses of the regulation and functions of the HuWRKY gene family.

Photo-assisted self-interference cancellation for in-band full-duplex radio-over-fiber system.

An optical approach to cancel the radio frequency self-interference for an in-band full-duplex radio-over-fiber system is proposed and experimentally demonstrated based on two Mach-Zehnder modulators and a balanced photodetector (BPD). The cancellation depth is larger than 50 dB and 24 dB for the single frequency and for a wideband signal, respectively. The application of the BPD eliminates the common mode noise and reduces no system flexibility because signal transmission is in one optical fiber by polarization multiplexing technology, instead of two fibers in the traditional self-interference cancellation system with a BPD. In addition, with no electrical delay and attenuation applied, the operational frequency band and cancellation depth are not confined by electronic devices.

The Potential of Gaseous Chlorine Dioxide for the Control of Citrus Postharvest Stem-End Rot Caused by Lasiodiplodia theobromae.

The focus of this study was to develop technologies using chlorine dioxide (ClO2) gas to control postharvest stem-end rot of citrus caused by Lasiodiplodia theobromae. Mycelial growth of L. theobromae on potato dextrose agar (PDA) plugs was completely inhibited by a 24-h ClO2 exposure provided by 0.5 g of solid ClO2 generating granular mixture in a 7.7-liter sealed container. In vivo experiments were conducted on artificially inoculated Tango and naturally infected U.S. Early Pride mandarins. When ClO2 treatments were initiated 0 to 6 h after inoculation, decay development was significantly reduced as compared with the control, and higher ClO2 doses were more effective. A ClO2 treatment (using 3 g of generating mixture per 7.7-liter sealed container) administered 0 h after inoculation resulted in 17.6% Diplodia stem-end rot incidence compared with 95.6% in the control, whereas the same treatment administered 24 h after inoculation was much less effective, resulting in 63.0% incidence compared with 85.4% in the control. Diplodia stem-end rot incidence of naturally infected fruit after using 6 or 9 g of generating mixture per 24-liter sealed box was 23.8 or 25.7%, respectively, compared with 47.9% for control fruit. The ClO2 treatments had no negative effects on fruit quality characteristics including weight loss, firmness, puncture resistance, titratable acids (TAs), total soluble solids (TSSs), and rind color. Albedo pH at wounds was significantly reduced from 6.0 to 4.8 by the ClO2 treatments, whereas undamaged albedo remained at 5.8. In addition, no visible physiologic defects, such as peel browning and bleaching, were observed on ClO2-treated fruit. These results indicate that ClO2 gas has the potential to be developed as a component of an integrated citrus postharvest decay control system to minimize fruit losses.

Genome-Wide Identification of Aquaporin Gene Family in Pitaya Reveals an HuNIP6;1 Involved in Flowering Process.

Aquaporins (AQPs) are essential membrane proteins involved in seed maturation and germination, stomata movement, photosynthesis, and regulation of plant flowering processes. Pitaya flowers are open at night and wither at daybreak, which shows an obvious circadian rhythm. In this study, a comprehensive genome-wide analysis of AQPs in Hylocereus undantus was conducted to screen key genes associated with flowering processes. A total of 33 HuAQP genes were identified from the H. undantus genome. The 33 HuAQPs were grouped into four subfamilies: 10 PIPs, 13 TIPs, 8 NIPs, and 2 SIPs, which were distributed on 9 out of 11 pitaya chromosomes (Chr) (except for Chr7 and Chr10). Results from expression profiles showed that HuNIP6;1 may be involved in pitaya's floral opening. HuNIP6;1 was localized exclusively in the cell membrane. Overexpression of HuNIP6;1 in Arabidopsis thaliana significantly promoted early flowering through regulating negative flowering regulators of MJM30, COL9, and PRR5, suggesting that HuNIP6;1 plays key roles in regulating flowering time. The present study provides the first genome-wide analysis of the AQP gene family in pitaya and valuable information for utilization of HuAQPs.

A Novel WRKY Transcription Factor HmoWRKY40 Associated with Betalain Biosynthesis in Pitaya (Hylocereus monacanthus) through Regulating HmoCYP76AD1.

Betalains are water-soluble nitrogen-containing pigments with multiple bioactivities. Pitaya is the only large-scale commercially grown fruit containing abundant betalains for consumers. However, the upstream regulators in betalain biosynthesis are still not clear. In this study, HmoWRKY40, a novel WRKY transcription factor, was obtained from the transcriptome data of pitaya (Hylocereus monacanthus). HmoWRKY40 is a member of the Group IIa WRKY family, containing a conserved WRKY motif, and it is located in the nucleus. The betalain contents and expression levels of HmoWRKY40 increased rapidly during the coloration of pitaya and reached their maximums on the 23rd day after artificial pollination (DAAP). Yeast one-hybrid and transient expression assays showed that HmoWRKY40 could bind and activate the promoter of HmoCYP76AD1. Silencing the HmoWRKY40 gene resulted in a significant reduction of betacyanin contents. These results indicate that HmoWRKY40 transcriptionally activates HmoCYP76AD, which is involved in the regulation of pitaya betalain biosynthesis. The results of the present study provide new regulatory networks related to betalain biosynthesis in pitaya.

Method for fast staining and obtaining high-magnification and high-resolution cell images of Nicotiana benthamiana.

As tools of plant molecular biology, fluorescence microscopy and Nicotiana benthamiana have been used frequently to study the structure and function of plant cells. However, it is difficult to obtain ideal micrographs; for example, the images are typically unclear, the inner cell structure cannot be observed under a high-power lens by fluorescence microscopy, etc. Here, we describe a method for observing the cell structure of N. benthamiana. This method significantly improves imaging by fluorescence microscopy and allows clear images to be obtained under a high-power lens. This method is easy to perform with good stability, and the stomatal structure, nucleus, nucleolus, chloroplast and other organelles in N. benthamiana cells as well as protein localizations and the locations of protein-protein interactions have been observed clearly. Furthermore, compared with traditional methods, fluorescent dye more efficiently dyes cells with this method. The applicability of this method was verified by performing confocal scanning laser microscopy (CSLM), and CSLM imaging was greatly improved. Thus, our results provided a method to visualize the subcellular structures of live cells in the leaves of N. benthamiana by greatly improving imaging under a fluorescence microscope and provided new insights and references for the study of cell structures and functions in other plants. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s12298-021-00931-5.

Integrated sRNAome and RNA-Seq analysis reveals miRNA effects on betalain biosynthesis in pitaya.

BACKGROUND: MicroRNAs (miRNAs) and their regulatory functions in anthocyanin, carotenoid, and chlorophyll accumulation have been extensively characterized in many plant species. However, the miRNA regulatory mechanism in betalain biosynthesis remains mostly unknown. RESULTS: In this study, 126 conserved miRNAs and 41 novel miRNAs were first isolated from Hylocereus monacanthus, among which 95 conserved miRNAs belonged to 53 miRNA families. Thirty-four candidate miRNAs related to betalain biosynthesis were differentially expressed. The expression patterns of those differential expressed miRNAs were analyzed in various pitaya tissues by RT-qPCR. A significantly negative correlation was detected between the expression levels of half those miRNAs and corresponding target genes. Target genes of miRNAs i.e. Hmo-miR157b-HmSPL6-like, Hmo-miR160a-Hpcyt P450-like3, Hmo-miR6020-HmCYP71A8-like, Hmo-novel-2-HmCYP83B1-like, Hmo-novel-15-HmTPST-like, Hmo-miR828a-HmTT2-like, Hmo-miR858-HmMYB12-like, Hmo-miR858-HmMYBC1-like and Hmo-miR858-HmMYB2-like were verified by 5'RACE and transient expression system in tobacco. CONCLUSIONS: Hmo-miR157b, Hmo-miR160a, Hmo-miR6020 Hmo-novel-2, Hmo-novel-15, Hmo-miR828a and Hmo-miR858 play important roles in pitaya fruit coloration and betalain accumulation. Our findings provide new insights into the roles of miRNAs and their target genes of regulatory functions involved in betalain biosynthesis of pitaya.

Photonic 2-D angle-of-arrival estimation based on an L-shaped antenna array for an early radar warning receiver.

Early radar warning is a significant step to lessen the fine scanning range of a receiver. The small size two-dimension (2-D) angle-of-arrival (AOA) estimation part with moderate accuracy and sensitivity is important for an early radar warning receiver. In our method, we specially design an L-shaped antenna array (L-sAA) and connect it with dual-polarization binary phase shift keying modulator (DP-BPSKM). The dual-sideband (DSB) modulation is performed to transfer most of the optical power to electrical, so as to increase the sensitivity. It is also possible to map the AOA information of the incoming beam to photo-detected electrical power without a high extinction ratio modulator or optical filter. During the estimation, the 2-D AOA is firstly measured, whose measurement range is 18.22°âˆ¼90° and the measurement error is lower than 1°. Then, based on the 2-D AOA estimation results, the third one is mathematically calculated to construct 3-D location of the target. Noteworthy, the amplitude comparison function (ACF) is adopted in this method to make the system response irrelative to the received signal power, which endows the system with signal power fluctuation immunity. Experimental results show that this method is capable of measuring a single-tone signal and a bandwidth signal. This structure is very concise and meets the potential of on-chip integration.

Simple approach for Doppler frequency shift estimation based on a dual-polarization quadrature phase shift keying (DP-QPSK) modulator.

A simple approach to estimating microwave Doppler frequency shift (DFS) based on a single dual-polarization quadrature phase shift keying (DP-QPSK) modulator is proposed and experimentally demonstrated. The scheme is capable of estimating both the value and direction of the DFS simultaneously and precisely owing to the introduction of the reference signal. In the proposed approach, the transmitted signal (microwave carrier) and the reference signal are loaded on the upper branch of the DP-QPSK modulator to generate carrier suppression double-sideband signals, respectively, while the echo signal is loaded on the lower branch of the DP-QPSK modulator to perform carrier suppression single-sideband modulation. Then optical sidebands of two branches are combined and sent to a low-speed photodetector to heterodyne. The value of the DFS is equivalent to the frequency of the beat signal between the transmitted and reference signals; meanwhile, the direction can be distinguished by comparing the frequency of the beat signal between the transmitted and reference signals with the frequency of the beat signal between the echo and reference signals. In the experiment, the accurate measurement of DFSs from $ - {100}\;{\rm kHz}$-100kHz to $ + {100}\;{\rm kHz}$+100kHz at the carrier frequencies of 15, 20, 35, and 39 GHz is implemented with errors less than $ \pm {10}\;{\rm Hz}$±10Hz.

The Role of EjSVPs in Flower Initiation in Eriobotrya japonica.

Flowering plants have evolved different flowering habits to sustain long-term reproduction. Most woody trees experience dormancy and then bloom in the warm spring, but loquat blooms in the cold autumn and winter. To explore its mechanism of flowering regulation, we cloned two SHORT VEGETATIVE PHASE (SVP) homologous genes from 'Jiefanzhong' loquat (Eriobotrya japonica Lindl.), namely, EjSVP1 and EjSVP2. Sequence analysis revealed that the EjSVPs were typical MADS-box transcription factors and exhibited a close genetic relationship with other plant SVP/DORMANCY-ASSOCIATED MADS-BOX (DAM) proteins. The temporal and spatial expression patterns showed that EjSVP1 and EjSVP2 were mainly expressed in the shoot apical meristem (SAM) after the initiation of flowering; after reaching their highest level, they gradually decreased with the development of the flower until they could not be detected. EjSVP1 expression levels were relatively high in young tissues, and EjSVP2 expression levels were relatively high in young to mature transformed tissues. Interestingly, EjSVP2 showed relatively high expression levels in various flower tissues. We analyzed the EjSVP promoter regions and found that they did not contain the C-repeat/dehydration-responsive element. Finally, we overexpressed the EjSVPs in wild-type Arabidopsis thaliana Col-0 and found no significant changes in the number of rosette leaves of Arabidopsis thaliana; however, overexpression of EjSVP2 affected the formation of Arabidopsis thaliana flower organs. In conclusion, EjSVPs were found to play an active role in the development of loquat flowering. These findings may provide a reference for exploring the regulation mechanisms of loquat flowering and the dormancy mechanisms of other plants.

12.5 Gb/s multi-channel broadcasting transmission for free-space optical communication based on the optical frequency comb module.

A wide-spectrum, ultra-stable optical frequency comb (OFC) module with 100 GHz frequency intervals based on a quantum dot mode locked (QDML) laser is fabricated by our lab, and a scheme with 12.5 Gb/s multi-channel broadcasting transmission for free-space optical (FSO) communication is proposed based on the OFC module. The output power of the OFC is very stable, with the specially designed circuit and the flatness of the frequency comb over the span of 6 nm, which can be limited to 1.5 dB. Four channel wavelengths are chosen to demonstrate one-to-many channels for FSO communication, like optical wireless broadcast. The outdoor experiment is established to test the bit error rate (BER) and eye diagrams with 12.5 Gb/s on-off keying (OOK). The indoor experiment is used to test the highest traffic rate, which is up to 21 Gb/s for one-hop FSO communication. To the best of our knowledge, this scheme is the first to propose the realization of one-to-many broadcasting transmission for FSO communication based on the OFC module. The advantages of integration, miniaturization, channelization, low power consumption, and unlimited bandwidth of one-to-many broadcasting communication scheme, shows promising results on constructing the future space-air-ground-ocean (SAGO) FSO communication networks.

40 km amplifier-less transmission of single wavelength 90 Gbps four-level pulse amplitude modulation signals enabled by an ultrabroadband directly modulated laser.

An ultrabroadband, high linearity directly modulated laser (DML) module operated at the O-band is proposed. The effect of the package network on the DML module is first investigated. In the package network, a wire bonding compensation method is used to improve the resonance at high frequency, which can be equivalent to the channel equalization technique. Without any optical amplification, we experimentally demonstrated 90 Gb/s four-level pulse amplitude modulation transmission over 40 km standard single mode fiber, which is the longest reach to the best of our knowledge. A bit error rate of 6.74×10-4 is achieved at a received optical power of -2.5 dBm. A receiver sensitivity of -4.5 dBm at 7% overhead forward error correction limit (3.8×10-3) is obtained for back-to-back with a power margin of more than 8.5 dB.