Study On Key Metabolic Pathways In Garlic Greening Process

Garlic(Allium Sativum L.)is a famous medicinal and edible plant.It not only has rich nutritional value,but also has the functions of sterilization,blood lipid reduction,anti-tumor,anti-liver disease,anti-diabetes,immune regulation and so on.However,garlic is prone to green discoloration during processing,which affects the garlic products quality and reduces the economic value of garlic products.Therefore,it is of great significance to study the key pathways and molecular biological mechanisms of garlic greening during garlic processing to prevent the greening phenomenon and maintain the quality of garlic.In this thesis,the key metabolic pathways and phenotypic analysis of garlic greening were investigated.The key metabolic pathways regulating garlic green discoloration were analyzed by transcriptomic and proteomic studies on the difference of green discoloration among different garlic varieties.The key metabolic pathway derived from transcriptomics and proteomics were verified by phenotypic analysis of different garlic varieties during the greening process.The main research results of this experiment are as follows:(1)Transcriptomic and proteomic analysis of Pizhou garlic and Laiwu Garlic was carried out by third-generation sequencing combined with second-generation sequencing and labeling free quantitative method.A total of 60087 unigenes were obtained,among which 30082 unigenes were annotated.Through differential gene analysis,there were 923 differentially expressed genes in Pizhou garlic and Laiwu garlic,of which 529 differentially expressed genes were up-regulated and 394 differentially expressed genes were down-regulated;Phenylpropane metabolic pathway was the most significant pathway for the enrichment of differentially expressed genes,which was found by KEGG and GO enrichment analysis.Proteomic analysis showed that there were 187 differentially expressed proteins,161up-regulated proteins and 26 down-regulated proteins between Pizhou garlic and Laiwu garlic;Differentially rich proteins were also significantly enriched in phenylpropane metabolic pathway,which was analyzed by KEGG and GO enrichment.The content of 10phenylpropane-related proteins in Pizhou garlic was significantly higher than that in Laiwu garlic;Ten candidate genes in phenylpropane pathway were selected for quantitative verification by q RT-PCR to verify the reliability of RNA-seq data.(2)The phenylpropane metabolic pathway during garlic greening was verified based on index measurement.The activities of phenylalanine ammoniase(PAL),cinnamate4-hydroxylase(CA4H)and 4-cardanate coenzyme A ligase(4CL)in pizhou garlic and Laiwu garlic were increased with the increase of greening degree of Pizhou garlic and Laiwu garlic.The contents of phenylalanine,phenolic acid(coumaric acid,ferulic acid,caffeic acid)and total phenol increased.In addition,?-glutathione aminotransferase activity and PBG content were also consistent with the intensity of green change.The green discoloration of the dormant garlic puree appears different amplitude increases and the non-dormant garlic puree did not appear green discoloration phenomenon when phenylalanine,cinnamic acid,p-coumaric acid,ferulic acid and caffeic acid were added to the dormant garlic puree and the non-dormant garlic puree.And the green discoloration degree of the dormant garlic puree occurs as phenolics content increases.Therefore,the key substances in phenylpropane pathway will promote garlic greening.