The CsDof1.8-CsLIPOXYGENASE09 module regulates C9 aroma production in cucumber.

Nine-carbon aldehydes and their relative alcohols (C9 aromas) are the main aroma compounds of cucumber (Cucumis sativus L.) fruits and provide a unique cucumber-like note. However, the key regulators of C9 aroma accumulation in cucumber fruit are poorly characterized. Based on C9 aroma dynamic analysis and transcriptome analysis during fruit development of two different cucumber inbred lines, Q16 and Q24, Lipoxygenase09 (CsLOX09) was identified as a candidate gene for C9 aroma accumulation. Additionally, Q24 with higher CsLOX09 expression accumulated more C9 aromas than Q16. To verify the function of CsLOX09, Cslox09 homozygote knockout lines were created. C9 aroma content decreased by 80.79%-99.16% in these mutants compared to the wild type. To further explore the reasons for the difference in CsLOX09 expression between Q16 and Q24 fruits, a co-expression network was constructed by integrating the C9 aroma-associated metabolism and transcriptomic data. Eighteen candidate transcription factors were highly correlated with the expression of CsLOX09. DNA binding with One Finger 1.8 (CsDof1.8) was confirmed to bind directly to the A/TAAAG motif of the CsLOX09 promoter through dual-luciferase, yeast one-hybrid, chromatin immunoprecipitation-qPCR and electrophoretic mobility shift assays. Furthermore, C9 aroma content and CsLOX09 expression were significantly increased in the CsDof1.8 overexpression lines. Overall, these data elucidate the metabolic regulation of C9 aromas in cucumber and provide a foundation for facilitating the regulation of flavor in cucumber breeding.

Enhanced preservation effects of clove (Syzygium aromaticum) essential oil on the processing of Chinese bacon (preserved meat products) by beta cyclodextrin metal organic frameworks (ß-CD-MOFs).

The applications of clove (Syzygium aromaticum) essential oil (CEO) are limited by instability, low solubility and high volatility. The present study aimed to improve the properties of CEO by microencapsulation with cyclodextrin metal organic frameworks (ß-CD-MOFs) to enhance the preservation effects on Chinese bacon (preserved meat products). The microencapsulated CEO by ß-CD-MOFs (CEO/ß-CD-MOFs) not only did not inhibit the antioxidant activities of CEO, but also showed significant improvements on their ROS scavenging abilities and thermo-/pH-stabilities. The increases of superoxide anion and hydroxyl radical scavenging activities were 20.74% and 12.84%, respectively. In addition, less lipid oxidation, including malondialdehyde (MDA) contents and peroxide values (POV), of Chinese bacon was found after the CEO/ß-CD-MOFs treatment than CEO and synthetic antioxidant (BHT) treatments. These results suggested the enhanced preservation effects of microencapsulated CEO on the processing of Chinese bacon and the great potential of ß-CD-MOFs as carriers for essential oils in food industry applications.

Transcriptomic and Histological Analysis of the Response of Susceptible and Resistant Cucumber to Meloidogyne incognita Infection Revealing Complex Resistance via Multiple Signaling Pathways.

The root-knot nematode (RKN), Meloidogyne incognita, is a devastating pathogen for cucumber (Cucumis sativus L.) specially in production under protected environments or continuous cropping. High level RKN resistance has been identified in African horned melon Cucumis metuliferus (CM). However, the resistance mechanism remains unclear. In this study, the comparative analysis on phenotypic and transcriptomic responses in the susceptible cucumber inbred line Q24 and the resistant CM, after M. incognita infection, was performed. The results showed that, in comparison with Q24, the CM was able to significantly reduce penetration numbers of second stage juveniles (J2), slow its development in the roots resulting in fewer galls and smaller giant cells suggesting the presence of host resistance in CM. Comparative transcriptomes analysis of Q24 and CM before and after M. incognita infection was conducted and differentially expressed genes (DEGs) associated with host resistance were identified in CM. Enrichment analyses revealed most enriched DEGs in Ca2+ signaling, salicylic acid (SA)/jamonate signaling (JA), as well as auxin (IAA) signaling pathways. In particular, in CM, DEGs in the Ca2+ signaling pathway such as those for the calmodulin and calcium-binding proteins were upregulated at the early stage of M. incognita infection; genes for SA/JA synthesis/signal transduction were markedly activated, whereas the IAA signaling pathway genes were inhibited upon infection suggesting the importance of SA/JA signaling pathways in mediating M. incognita resistance in CM. A model was established to explain the different molecular mechanisms on M. incognita susceptibility in cucumber and resistance to M. incognita infection in CM.

Redox Status, JA and ET Signaling Pathway Regulating Responses to Botrytis cinerea Infection Between the Resistant Cucumber Genotype and Its Susceptible Mutant.

Botrytis cinerea is an important necrotrophic fungal pathogen with a broad host range and the ability to causing great economic losses in cucumber. However, the resistance mechanism against this pathogen in cucumber was not well understood. In this study, the microscopic observation of the spore growth, redox status measurements and transcriptome analysis were carried out after Botrytis cinerea infection in the resistant genotype No.26 and its susceptible mutant 26M. Results revealed shorter hypha, lower rate of spore germination, less acceleration of H2O2, O2 -, and lower total glutathione content (GSH+GSSG) in No.26 than that in 26M, which were identified by the staining result of DAB and NBT. Transcriptome data showed that after pathogen infection, a total of 3901 and 789 different expression genes (DEGs) were identified in No.26 and 26M respectively. These DEGs were highly enriched in redox regulation pathway, hormone signaling pathway and plant-pathogen interaction pathway. The glutathione S-transferase genes, putative peroxidase gene, and NADPH oxidase were up-regulated in No.26 whereas these genes changed little in 26M after Botrytis cinerea infection. Jasmonic acid and ethylene biosynthesis and signaling pathways were distinctively activated in No.26 comparing with 26M upon infection. Much more plant defense related genes including mitogen-activated protein kinases, calmodulin, calmodulin-like protein, calcium-dependent protein kinase, and WRKY transcription factor were induced in No.26 than 26M after pathogen infection. Finally, a model was established which elucidated the resistance difference between resistant cucumber genotype and susceptible mutant after B. cinerea infection.