R2R3-MYB transcription factor CsMYB60 controls mature fruit skin color by regulating flavonoid accumulation in cucumber.

Skin color is an important trait that determines the cosmetic appearance and quality of fruits. In cucumber, the skin color ranges from white to brown in mature fruits. However, the genetic basis for this important trait remains unclear. We conducted a genome-wide association study of natural cucumber populations, along with map-based cloning techniques, on an F2 population resulting from a cross between Pepino (with yellow-brown fruit skin) and Zaoer-N (with creamy fruit skin). We identified CsMYB60 as a candidate gene responsible for skin coloration in mature cucumber fruits. In cucumber accessions with white to pale yellow skin color, a premature stop mutation (C to T) was found in the second exon region of CsMYB60, whereas light yellow cucumber accessions exhibited splicing premature termination caused by an intronic mutator-like element insertion in CsMYB60. Transgenic CsMYB60c cucumber plants displayed a yellow-brown skin color by promoting accumulation of flavonoids, especially hyperoside, a yellow-colored flavonol. CsMYB60c encodes a nuclear protein that primarily acts as a transcriptional activator through its C-terminal activation motif. RNA sequencing and DNA affinity purification sequencing assays revealed that CsMYB60c promotes skin coloration by directly binding to the YYTACCTAMYT motif in the promoter regions of flavonoid biosynthetic genes, including CsF3'H, which encodes flavonoid 3'-hydroxylase. The findings of our study not only offer insight into the function of CsMYB60 as dominantly controlling fruit coloration, but also highlight that intronic DNA mutations can have a similar phenotypic impact as exonic mutations, which may be valuable in future cucumber breeding programs.

Cucumber JASMONATE ZIM-DOMAIN 6 interaction with transcription factor MYB6 impairs waterlogging-triggered adventitious rooting.

Waterlogging is a serious abiotic stress that drastically decreases crop productivity by damaging the root system. Jasmonic acid (JA) inhibits waterlogging-induced adventitious root (AR) formation in cucumber (Cucumis sativus L.). However, we still lack a profound mechanistic understanding of how JA governs AR formation under waterlogging stress. JAZ (JASMONATE ZIM-DOMAIN) proteins are responsible for repressing JA signaling in a transcriptional manner. In this study, we showed that overexpressing CsJAZ8 inhibited the formation of ARs triggered by waterlogging. Molecular analyses revealed that CsJAZ8 inhibited the activation of the R2R3-MYB transcription factor CsMYB6 via direct interaction. Additionally, silencing of CsMYB6 negatively impacted AR formation under waterlogging stress, as CsMYB6 could directly bind to the promoters of 1-aminocyclopropane-1-carboxylate oxidase2 gene CsACO2 and gibberellin 20-oxidases gene CsGA20ox2, facilitating the transcription of these genes. The overexpression of CsACO2 and CsGA20ox2 led to increased levels of ethylene and gibberellin, which facilitated AR formation under waterlogging conditions. On the contrary, silencing these genes resulted in contrasting phenotypes of AR formation. These results highlight that the transcriptional cascade of CsJAZ8 and CsMYB6 plays a critical role in regulating hormonal-mediated cucumber waterlogging-triggered AR formation by inhibiting ethylene and gibberellin accumulation. We anticipate that our findings will provide insights into the molecular mechanisms that drive the emergence of AR in cucumber plants under waterlogging stress.

Cucumber abscisic acid 8'-hydroxylase Csyf2 regulates yellow flesh by modulating carotenoid biosynthesis.

Cucumber (Cucumis sativus L.) flesh is typically colorless or pale green. Flesh with yellow or orange pigment, determined mainly by carotenoid content and composition, is mostly found in semi-wild Xishuangbanna cucumber, which has a very narrow genetic background. Here, we identified a spontaneous cucumber mutant with yellow flesh (yf-343), which accumulated more ß-cryptoxanthin and less lutein than regular cultivated European glasshouse-type cucumbers. Genetic analysis revealed that the yellow flesh phenotype was controlled by a single recessive gene. Through fine mapping and gene sequencing, we identified the candidate gene C. sativus yellow flesh 2 (Csyf2), encoding an abscisic acid (ABA) 8'-hydroxylase. Overexpression and RNAi-silencing of Csyf2 in cucumber hairy roots produced lower and higher ABA contents than in non-transgenic controls, respectively. Further, RNA-seq analysis suggested that genes related to ABA signal transduction were differentially expressed in fruit flesh between yf-343 and its wild type, BY, with white flesh. The carotenoid biosynthesis pathway was specifically enriched in fruit flesh at 30 days after pollination when yf-343 fruit flesh turns yellow. Our findings highlight a promising target for gene editing to increase carotenoid content, expanding our genetic resources for pigmented cucumber flesh breeding for improving the nutritional quality of cucumber.

A review on surfactin: molecular regulation of biosynthesis.

Surfactin has many biological activities, such as inhibiting plant diseases, resisting bacteria, fungi, viruses, tumors, mycoplasma, anti-adhesion, etc. It has great application potential in agricultural biological control, clinical medical treatment, environmental treatment and other fields. However, the low yield has been the bottleneck of its popularization and application. It is very important to understand the synthesis route and control strategy of surfactin to improve its yield and purity. In this paper, based on the biosynthetic pathway and regulatory factors of surfactin, its biosynthesis regulation strategy was comprehensively summarized, involving enhancement of endogenous and exogenous precursor supply, modification of the synthesis pathway of lipid chain and peptide chain, improvement of secretion and efflux, and manipulation some global regulatory factors, such as Spo0A, AbrB, ComQXP, phrCSF, etc. to directly or indirectly stimulate surfactin synthesis. And the current production and separation and purification process of surfactin are briefly described. This review also provides a scientific reference for promoting surfactin production and its applications in various fields.

A review of recent progress in the application of Raman spectroscopy and SERS detection of microplastics and derivatives.

The global environmental concern surrounding microplastic (MP) pollution has raised alarms due to its potential health risks to animals, plants, and humans. Because of the complex structure and composition of microplastics (MPs), the detection methods are limited, resulting in restricted detection accuracy. Surface enhancement of Raman spectroscopy (SERS), a spectral technique, offers several advantages, such as high resolution and low detection limit. It has the potential to be extensively employed for sensitive detection and high-resolution imaging of microplastics. We have summarized the research conducted in recent years on the detection of microplastics using Raman and SERS. Here, we have reviewed qualitative and quantitative analyses of microplastics and their derivatives, as well as the latest progress, challenges, and potential applications.

Synthesis of nanoparticles via microfluidic devices and integrated applications.

In recent years, nanomaterials have attracted the research intervention of experts in the fields of catalysis, energy, biomedical testing, and biomedicine with their unrivaled optical, chemical, and biological properties. From basic metal and oxide nanoparticles to complex quantum dots and MOFs, the stable preparation of various nanomaterials has always been a struggle for researchers. Microfluidics, as a paradigm of microscale control, is a remarkable platform for online stable synthesis of nanomaterials with efficient mass and heat transfer in microreactors, flexible blending of reactants, and precise control of reaction conditions. We describe the process of microfluidic preparation of nanoparticles in the last 5 years in terms of microfluidic techniques and the methods of microfluidic manipulation of fluids. Then, the ability of microfluidics to prepare different nanomaterials, such as metals, oxides, quantum dots, and biopolymer nanoparticles, is presented. The effective synthesis of some nanomaterials with complex structures and the cases of nanomaterials prepared by microfluidics under extreme conditions (high temperature and pressure), the compatibility of microfluidics as a superior platform for the preparation of nanoparticles is demonstrated. Microfluidics has a potent integration capability to combine nanoparticle synthesis with real-time monitoring and online detection, which significantly improves the quality and production efficiency of nanoparticles, and also provides a high-quality ultra-clean platform for some bioassays.

Transcriptome analysis of the production enhancement mechanism of antimicrobial lipopeptides of Streptomyces bikiniensis HD-087 by co-culture with Magnaporthe oryzae Guy11.

The lipopeptides produced by Streptomyces bikiniensis have a significant inhibitory effect on Magnaporthe oryzae, but the low yield limits its application. In this study, the anti-M. oryzae activity of the broth of S. bikiniensis HD-087 co-cultured with M. oryzae Guy11 mycelium has risen by 41.22% compared with pure culture, and under induction conditions of adding Guy11-inducer (cell-free supernatant of M. oryzae Guy11), the activity of strain HD-087 improved 61.76%. The result proved that the enhancement effect of Guy11 on the antimicrobial activity of HD-087 was mainly related to metabolites but mycelium cells. Under optimum induction conditions, NRPS gene expression levels of HD-087 were significantly increased by induction with Guy11-inducer, the biomass of HD-087 had no significant change, but crude extract of lipopeptide (CEL) production was 107.4% higher than pure culture, and TLC result under acid hydrolysis showed that the induced culture has one component more than pure culture. To clarify the regulation mechanism of improving lipopeptide production of HD-087 with Guy11-inducer, transcriptomic analysis was performed using RNAseq to compare the induced culture and pure culture. In the induced culture, 943 genes were up-regulated, while 590 genes were down-regulated in DEGs (differentially expressed genes). KEGG results showed that the expression of genes related to amino acid synthesis, fatty acid metabolism, TCA cycle and pyruvate metabolism pathway were significantly increased. The increased expression of genes related to these metabolic pathways provided sufficient precursors for lipopeptide synthesis. Accordingly, key enzyme genes responsible for the synthesis of lipopeptides Srf and NRPS was significantly increased. Quorum sensing related genes OppA and MppA were significantly up-regulated, and then ComP was activated and promoted lipopeptide synthesis. These results provided a scientific basis for using M. oryzae to induce the increase of the production of Streptomyces lipopeptides, and also laid a foundation for further exploring the co-culture mechanisms among different genera.

Nitric Oxide Extends the Postharvest Life of Water Bamboo Shoots Partly by Maintaining Mitochondrial Structure and Energy Metabolism.

Harvested water bamboo shoots can be stored for only a few days before they lose weight and become soft. Nitrogen oxide (NO) and modified atmosphere packaging (MAP) have previously been used to prolong horticultural crop storage. In the present study, we analyzed the joint effect of these two methods on extending the postharvest quality of water bamboo shoots. Water bamboo shoots were treated with (1) 30 µL L-1 NO, (2) MAP, and (3) a combination of NO and MAP. The NO treatment delayed the softness and weight loss through maintaining the integrity of the mitochondrial ultrastructure and enhancing the ATP level by activating the expressions and activities of succinic dehydrogenase, malic acid dehydrogenase, and cytochrome oxidase. MAP improved the effect of NO on the mitochondrial energy metabolism. These results indicate that NO and MAP treatments are effective at suppressing the quality deterioration of water bamboo shoots, MAP improves the effect of NO in extending postharvest life, and NO may be the main effective factor in the combination of NO and MAP.

Dual-wavelength excitation combined Raman spectroscopy for detection of highly fluorescent samples.

As fluorescence is the major limitation in Raman scattering, near-infrared excitation wavelength (>780nm) is preferred for fluorescence suppression in Raman spectroscopy. To reduce the risk of fluorescence interference, we developed a dual-wavelength excitation combined Raman spectroscopy (DWECRS) system at 785 and 830 nm. By a common optical path, each laser beam was focused on the same region of the sample by a single objective lens, and the dual-wavelength excitation Raman spectra were detected by a single CCD detector; in addition, 785 and 830 nm excitation Raman spectra can be directly constructed as combined Raman spectrum in the DWECRS system. The results of pure peanut oil and glycerol indicate that the combined Raman spectrum cannot only reduce fluorescence interference but also keep a high signal-to-noise ratio in the high-wavenumber region. The results of dye-ethanol solutions with different concentrations show that the handheld DWECRS system can be used as a smart method to dodge strong fluorescence. Furthermore, we developed a peak intensity ratio method with the DWECRS system to distinguish different types of edible oils. The peak intensity ratio distribution chart of edible oils showed each oil normalized center was relatively independent and nonoverlapped, which can be used as the basis of edible oil classification analysis. In the future, the DWECRS system has potential to be used as a tool for more complex applications.

Surface-enhanced shifted excitation Raman difference spectroscopy for trace detection of fentanyl in beverages.

In recognition of the misuse risks of fentanyl, there is an urgent need to develop a useful and rapid analytical method to detect and monitor the opioid drug. The surface-enhanced shifted excitation Raman difference spectroscopy (SE-SERDS) method has been demonstrated to suppress background interference and enhance Raman signals. In this study, the SE-SERDS method was used for trace detection of fentanyl in beverages. To prepare the simulated illegal drug-beverages, fentanyls were dissolved into distilled water or Mizone as a series of test samples. Based on our previous work, the surface-enhanced Raman spectroscopy detection was performed on the beverages containing fentanyl by the prepared AgNPs and the SE-SERDS spectra of test samples were collected by the dual-wavelength rapid excitation Raman difference spectroscopy system. In addition, the quantitative relationship between fentanyl concentrations and the Raman peaks was constructed by the Langmuir equation. The experimental results show that the limits of quantitation for fentanyl in distilled water and Mizone were 10 ng/mL and 200 ng/mL, respectively; the correlation coefficients for the nonlinear regression were as high as 0.9802 and 0.9794, respectively; and the relative standard deviation was less than 15%. Hence, the SE-SERDS method will be a promising method for the trace analyses of food safety and forensics.

The major-effect quantitative trait locus Fnl7.1 encodes a late embryogenesis abundant protein associated with fruit neck length in cucumber.

Fruit neck length (FNL) is an important quality trait in cucumber because it directly affects its market value. However, its genetic basis remains largely unknown. We identified a candidate gene for FNL in cucumber using a next-generation sequencing-based bulked segregant analysis in F2 populations, derived from a cross between Jin5-508 (long necked) and YN (short necked). A quantitative trait locus (QTL) on chromosome 7, Fnl7.1, was identified through a genome-wide comparison of single nucleotide polymorphisms between long and short FNL F2 pools, and it was confirmed by traditional QTL mapping in multiple environments. Fine genetic mapping, sequences alignment and gene expression analysis revealed that CsFnl7.1 was the most likely candidate Fnl7.1 locus, which encodes a late embryogenesis abundant protein. The increased expression of CsFnl7.1 in long-necked Jin5-508 may be attributed to mutations in the promoter region upstream of the gene body. The function of CsFnl7.1 in FNL control was confirmed by its overexpression in transgenic cucumbers. CsFnl7.1 regulates fruit neck development by modulating cell expansion. Probably, this is achieved through the direct protein-protein interactions between CsFnl7.1 and a dynamin-related protein CsDRP6 and a germin-like protein CsGLP1. Geographical distribution differences of the FNL phenotype were found among the different cucumber types. The East Asian and Eurasian cucumber accessions were highly enriched with the long-necked and short-necked phenotypes, respectively. A further phylogenetic analysis revealed that the Fnl7.1 locus might have originated from India. Thus, these data support that the CsFnl7.1 has an important role in increasing cucumber FNL.

Sugar enhances waterlogging-induced adventitious root formation in cucumber by promoting auxin transport and signalling.

Waterlogging is a severe environmental stress that causes severe crop productivity losses. Cucumber (Cucumis sativus L.) survives waterlogging by producing adventitious roots (ARs) that enhance gas exchange. Little is known about the role of light and sugars in the waterlogging-induced production of ARs. The role of these factors in AR production was therefore studied in cucumber seedlings grown in the absence or presence of waterlogging and different light conditions. The effect of photosynthesis was studied by removing the shoots of the seedlings and replacing them with exogenous applications of sucrose or stachyose. Shoot removal inhibited AR emergence and elongation. However, the exogenous application of sugars fully restored AR emergence and partially restored root elongation. The exogenous application of a synthetic auxin restored AR emergence but not AR elongation. Transcriptome profiling analysis was used to determine the effects of light on gene expression in the hypocotyls under these conditions. The levels of transcripts encoding proteins involved in auxin transport and signalling were higher in the light and following the exogenous application of sucrose and stachyose. These results show that the waterlogging-induced emergence of ARs is regulated by the interaction between sugars and auxin, whereas AR elongation depends only on sugars alone.

Differences in xylem development between Dutch and Japanese tomato (Solanum lycopersicum) correlate with cytokinin levels in hypocotyls.

BACKGROUND AND AIMS: Dutch tomato cultivars tend to have a greater yield than Japanese cultivars even if they are grown under the same conditions. Factors contributing to the increased yield of the Dutch cultivars were a greater light use efficiency and greater leaf photosynthetic rate. On the other hand, the relationship between tomato yields and anatomical traits is still unclear. The aim of this study is to identify the anatomical traits related to the difference in yield between Dutch and Japanese cultivars. METHODS: Anatomical properties were compared during different growth stages of Dutch and Japanese tomatoes. Hormone profiles and related gene expression in hypocotyls of Dutch and Japanese cultivars were compared in the hypocotyls of 3- and 4-week-old plants. KEY RESULTS: Dutch cultivars have a more developed secondary xylem than Japanese cultivars, which would allow for greater transport of water, mineral nutrients and phytohormones to the shoots. The areas and ratios of the xylem in the hypocotyls of 3- to 6-week-old plants were larger in the Dutch cultivars. In reciprocal grafts of the Japanese and Dutch cultivars, xylem development at the scion and rootstock depended on the scion cultivar, suggesting that some factors in the scion are responsible for the difference in xylem development. The cytokinin content, especially the level of N6-(Δ 2-isopentenyl) adenine (iP)-type cytokinin, was higher in the Dutch cultivars. This result was supported by the greater expression of Sl-IPT3 (a cytokinin biosynthesis gene) and Sl-RR16/17 (a cytokinin-responsive gene) in the Dutch cultivars. CONCLUSIONS: These results suggest that iP-type cytokinins, which are locally synthesized in the hypocotyl, contribute to xylem development. The greater xylem development in Dutch cultivars might contribute to the high yield of the tomato.

The major-effect quantitative trait locus CsARN6.1 encodes an AAA ATPase domain-containing protein that is associated with waterlogging stress tolerance by promoting adventitious root formation.

In plants, the formation of hypocotyl-derived adventitious roots (ARs) is an important morphological acclimation to waterlogging stress; however, its genetic basis remains fragmentary. Here, through combined use of bulked segregant analysis-based whole-genome sequencing, SNP haplotyping and fine genetic mapping, we identified a candidate gene for a major-effect QTL, ARN6.1, that was responsible for waterlogging tolerance due to increased AR formation in the cucumber line Zaoer-N. Through multiple lines of evidence, we show that CsARN6.1 is the most possible candidate for ARN6.1 which encodes an AAA ATPase. The increased formation of ARs under waterlogging in Zaoer-N could be attributed to a non-synonymous SNP in the coiled-coil domain region of this gene. CsARN6.1 increases the number of ARs via its ATPase activity. Ectopic expression of CsARN6.1 in Arabidopsis resulted in better rooting ability and lateral root development in transgenic plants. Transgenic cucumber expressing the CsARN6.1Asp allele from Zaoer-N exhibited a significant increase in number of ARs compared with the wild type expressing the allele from Pepino under waterlogging conditions. Taken together, these data support that the AAA ATPase gene CsARN6.1 has an important role in increasing cucumber AR formation and waterlogging tolerance.

Waterlogging-induced adventitious root formation in cucumber is regulated by ethylene and auxin through reactive oxygen species signalling.

Development of adventitious roots (ARs) at the base of the shoot is an important adaptation of plants to waterlogging stress; however, its physiological mechanisms remain unclear. Here, we investigated the regulation of AR formation under waterlogged conditions by hormones and reactive oxygen species (ROS) in Cucumis sativus L., an agriculturally and economically important crop in China. We found that ethylene, auxin, and ROS accumulated in the waterlogged cucumber plants. On the other hand, application of the ethylene receptor inhibitor 1-methylcyclopropene (1-MCP), the auxin transport inhibitor 1-naphthylphthalamic acid (NPA), or the NADPH oxidase inhibitor diphenyleneiodonium (DPI) decreased the number of ARs induced by waterlogging. Auxin enhanced the expression of ethylene biosynthesis genes, which led to ethylene entrapment in waterlogged plants. Both ethylene and auxin induced the generation of ROS. Auxin-induced AR formation was inhibited by 1-MCP, although ethylene-induced AR formation was not inhibited by NPA. Both ethylene- and auxin-induced AR formation were counteracted by DPI. These results indicate that auxin-induced AR formation is dependent on ethylene, whereas ethylene-induced AR formation is independent of auxin. They also show that ROS signals mediate both ethylene- and auxin-induced AR formation in cucumber plants.

Sequence and Structural Analysis of AA9 and AA10 LPMOs: An Insight into the Basis of Substrate Specificity and Regioselectivity.

Lytic polysaccharide monooxygenases (LPMOs) are key enzymes in both the natural carbon cycle and the biorefinery industry. Understanding the molecular basis of LPMOs acting on polysaccharide substrates is helpful for improving industrial cellulase cocktails. Here we analyzed the sequences, structures, and substrate binding modes of LPMOs to uncover the factors that influence substrate specificity and regioselectivity. Our results showed that the different compositions of a motif located on L2 affect the electrostatic potentials of substrate binding surfaces, which in turn affect substrate specificities of AA10 LPMOs. A conserved Asn at a distance of 7 Å from the active center Cu might, together with the conserved Ser immediately before the second catalytic His, determine the localization of LPMOs on substrate, and thus contribute to C4-oxidizing regioselectivity. The findings in this work provide an insight into the molecular basis of substrate specificity and regioselectivity of LPMOs.

[Risk assessment for emergency events of infectious disease in outlying areas of large-scale activities].

OBJECTIVE: To identify and assess the potential public health risks of emergency events of infectious disease in the surrounding areas of Hangzhou during the 11th G20 summit, and to assess their impacts on the G20 summit. METHODS: The surrounding cities of Hangzhou included Ningbo, Wenzhou, Jiaxing, Huzhou, Shaoxing, Jinhua, Quzhou, Zhoushan, Taizhou and Lishui. Background information on infectious diseases in Zhejiang province was collected, and the brainstorming and expert consultation methods were used to identify the risks. The local risks and the impact of local risks on the G20 summit were assessed. RESULTS: The criteria for public health risk was first established. Through the assessments,a total of 27 kinds of infectious diseases in 4 types of public health risks were identified. The impact of these risks on Hangzhou G20 summit was divided into 1 item of high-risk, 12 items of medium risk and 14 items of low risk.According to the results of risk assessment, the recommendations for risk management of respiratory infectious diseases, intestinal infectious diseases, imported infectious diseases like Middle East respiratory syndrome and other infectious diseases were made. With risk management, Middle East respiratory syndrome was not occurred during the G20 summit, and the epidemic situation of other infectious diseases with middle or low risks was almost the same with that of past years. CONCLUSIONS: sThe public health risks of Hangzhou G20 summit from sudden infectious diseases in outlying areas are mainly medium and low risks. The recommendations on risk management provide a basis for reducing the adverse consequences of public health risks in the event of an outbreak of infectious diseases, avoiding the impact of various risk factors in the outlying areas on G20 summit.

Elucidation of the molecular responses of a cucumber segment substitution line carrying Pm5.1 and its recurrent parent triggered by powdery mildew by comparative transcriptome profiling.

BACKGROUND: Powdery mildew (PM) is one of the most severe fungal diseases of cucurbits, but the molecular mechanisms underlying PM resistance in cucumber remain elusive. In this study, we developed a PM resistant segment substitution line SSL508-28 that carried a segment on chromosome five representing the Pm5.1 locus from PM resistant donor Jin5-508 using marker-assisted backcrossing of an elite PM susceptible cucumber inbred line D8. RESULTS: Whole-genome resequencing of SSL508-28, Jin5-508 and D8 was performed to identify the exact boundaries of the breakpoints for this introgression because of the low density of available single sequence repeat markers. This led to the identification of a ~6.8 Mb substituted segment predicted to contain 856 genes. RNA-seq was used to study gene expression differences in PM treated (plants harvested 48 h after inoculation) and untreated (control) SSL508-28 and D8 lines. Exactly 1,248 and 1,325 differentially expressed genes (DEGs) were identified in SSL508-28 and D8, respectively. Of those, 88 DEGs were located in the ~6.8 Mb segment interval. Based on expression data and annotation, we identified 8 potential candidate genes that may participate in PM resistance afforded by Pm5.1, including two tandemly arrayed genes encoding receptor protein kinases, two transcription factors, two genes encoding remorin proteins, one gene encoding a P-type ATPase and one gene encoding a 70 kDa heat shock protein. The transcriptome data also revealed a complex regulatory network for Pm5.1-mediated PM resistance that may involve multiple signal regulators and transducers, cell wall modifications and the salicylic acid signaling pathway. CONCLUSION: These findings shed light on the cucumber PM defense mechanisms mediated by Pm5.1 and provided valuable information for the fine mapping of Pm5.1 and breeding of cucumber with enhanced resistance to PM.

Comparative RNA-seq based transcriptome profiling of waterlogging response in cucumber hypocotyls reveals novel insights into the de novo adventitious root primordia initiation.

BACKGROUND: Waterlogging is a serious abiotic stress to plant growth because it results in the decline in the supplement of oxygen to submerged tissues. Although cucumber (Cucumis sativus L.) is sensitive to waterlogging, its ability to generate adventitious roots (ARs) facilitates gas diffusion and increases plant survival when the oxygen concentration is decreased. To gain a better understanding of the molecular mechanisms that enable de novo AR primordia emergence upon waterlogging, the RNA sequencing-based transcriptomic responses of two contrasting cucumber genotypes, Zaoer-N (waterlogging tolerant) and Pepino (waterlogging sensitive), which differed in their abilities to form AR were compared. RESULTS: More than 27,000 transcripts were detected in cucumber hypocotyls, from which 1494 and 1766 genes in 'Zaoer-N' and 'Pepino', respectively, were differentially expressed 2 days after waterlogging. The significant positive correlation between RNA sequencing data and a qPCR analysis indicated that the identified genes were credible. A comparative analysis revealed that genes functioning in carbohydrate mobilization, nitrate assimilation, hormone production and signaling pathways, transcription factors and cell division might contribute to the waterlogging-triggered AR primordia initiation. Ethylene was determined to be an important plant hormone responsible for the cucumber ARs initiation. Additionally, genes encoding cytochrome P450, ankyrin repeat-containing proteins and sulfite oxidases were determined as important in waterlogging acclimation. CONCLUSION: This research broadens our understanding of the mechanism underlying waterlogging-triggered ARs emergence, and provides valuable information for the breeding of cucumber with enhanced waterlogging tolerance.

Inheritance and quantitative trail loci mapping of adventitious root numbers in cucumber seedlings under waterlogging conditions.

The hypocotyl-derived adventitious root (AR) is an important morphological acclimation to waterlogging stress; however, its genetic basis has not been adequately understood. In the present study, a mixed major gene plus polygene inheritance model was used to analyze AR numbers (ARN) 7 days after waterlogging treatment in six generations (P1, P2, F1, B1, B2, and F2), using cucumber waterlogging tolerant line Zaoer-N and sensitive Pepino as parents. The results showed that the genetic model D-4, mixed one negative dominance major gene and additive-dominance polygenes, is the best-fitting genetic model for waterlogging-triggered ARN phenotype. A genetic linkage map spanning 550.8 cM and consisting of 149 simple sequence repeat (SSR) markers segregating into seven linkage groups was constructed. Three QTLs (ARN3.1, ARN5.1, and ARN6.1) distributed on chromosomes 3, 5, and 6 were identified by composite interval mapping. The major-effect QTL, ARN6.1, located between SSR12898 and SSR04751, was the only locus detected in three seasons, with least likelihood (LOD) scores of 8.8, 10.4, and 9.5 and account for 17.6, 24, and 19.8% of the phenotypic variance, respectively. Using five additional single nucleotide polymorphism (SNP) makers, the ARN6.1 was narrowed down to a 0.79 Mb interval franked by SSR12898 and SNP25558853. Illumina RNA-sequencing data generated on hypocotyls of two parents 48 h after waterlogging treatment revealed 15 genes in the 0.79 Mb interval were differentially expressed, including Csa6G503880 encoding a salicylic acid methyl transferase-like protein, Csa6G504590 encoding a cytochrome P450 monooxygenase, and Csa6G505230 encoding a heavy metal-associated protein. Our findings shed light on the genetic architecture underlying adventitious rooting during waterlogging stress in cucumber, and provide a list of potential gene targets for further elucidating waterlogging tolerance in plants.