Transcriptome Analysis Of Lepidium Meyenii Walp. And Accumulation Of Benzylglucosinolates During Post-harvest Cryopreservation

Lepidium Meyenii Walp.is a kind of medicinal and edible plant with very high economic value.Macamides are a unique and iconic component only found in Maca.Moreover,benzyl glucosinolates are the precursor of macamides synthesis in the drying process,which directly affect the content of macamides,and then control the quality of Maca.At the same time,benzyl glucosinolates and their metabolites are also the main bioactive components of Maca,which have the potential effects of anti-fatigue,anti-tumor,improving fertility and neuroprotection.Therefore,the accumulation and metabolism of benzyl glucosinolates should be paid special attention in Maca planting,harvesting and storage.In the early stage of our research group,we found that benzyl glucosinolate content have a significant increase under the condition of low temperature storage,and the dynamic tracking and regulation network related to benzyl glucosinolates accumulation under the low temperature stress have not been reported yet.In this study,the correlation between amino acid,glucose,plant hormone and other metabolic components with benzyl glucosinolate accumulation during 4°C cryopreservation was discussed.Fresh Maca and Maca stored in 4 °C for 2 days(high benzyl glucosinolate period),Maca stored in 4 °C for 10 days(low benzyl glucosinolate period)are as a material for transcriptome analysis.The main results of the analysis of possible metabolic regulatory mechanism under low temperature stress,as follows:(1)The optimal storage temperature for the accumulation of benzylglucosinolates in fresh Maca root after harvest was determined.Combined with benzyl glucosinolate content changes and mass loss rate,relative conductivity changes,while Maca stored in 20 ° C,4 ° C,-4 ° C and-20 ° C for 2 months.We found that the relative conductivity increased significantly with the storage time at 4 °C and-20 °C,and the effect on cell membrane permeability was extremely significant,indicating that the damage to cell was relatively serious.Through the mass loss rate and relative conductivity of Maca at 20 °C room temperature storage,we found that the conductivity is sharply increased,and the cell membrane structure is seriously damaged.The mass loss rate and relative conductivity of the Maca are relatively low at 4 °C.At the four temperatures,the content of benzyl glucosinolates showed a fluctuating change.At 4 °C and 20 °C,the benzyl glucosinolates showed a more significant step-wise increase.Therefore,considering the comprehensive quality of Maca in storage,it is finally showed that 4 °C is the optimal storage temperature for the accumulation of benzyl glucosinolates.(2)Through the correlation analysis between amino acid,glucose,plant hormone and other metabolic components with benzyl glucosinolates accumulation during 4 °C cryopreservation,the important metabolic components of benzylglucosinolates accumulation during storage were preliminarily determined.It was found that the content of benzyl glucosinolate was positively correlated with phenylalanine content during storage at 4 °C(R=0.614,P=0.013<0.05),and it was significantly positively correlated with glucose content(R=0.731,P=0.002<0.01),while gibberellin and jasmonic acid content were significantly negatively correlated with benzyl glucosinolate content(R values were-0.515,-0.564;P values were less than 0.05),while myrosinase activity,abscisic acid,salicylic acid content was no significant correlation between and benzyl glucosinolate content.(3)A possible metabolic regulatory mechanism for the accumulation of Maca benzyl glucosinolate under low temperature stress was constructed.This study performed transcriptome sequencing analysis on fresh Maca,2 days storage of Maca(high benzyl glucosinolate period)at 4 °C,and storage of 10 days of Maca(low benzyl glucosinolate period)at 4 ° C.The DEGs of Freshs-vs-Storage 2ds,Freshs-vs-Storage 10 ds and Storage 2ds-vs-Storage 10 ds identified 16,626,15,613,and 6,126 respectively.We found that a large number of differential functional genes are associated with stress responses.Most of these genes are significantly enriched in plant circadian rhythm,plant-pathogen interaction,plant hormone signal transduction and secondary metabolite biosynthesis.Benzyl glucosinolate accumulation may be through ABA signaling molecules and CBFs signal transduction pathway under low temperature stress,after a series of intracellular reaction(such as sugar regulation),and then through hormone transduction pathway(ABA,SA,etc.)transfer,activate the expression of transcription factors MYB,WRKY,bZIP,DOF,etc.,which regulate the accumulation of benzyl glucosinolates.Finallyi it up-regulate or down-regulate the genes involved in the synthesis and degradation of benzyl glucosinolates,thereby responding to cold signals,resulting in benzyl glucosinolates accumulation under low temperature stress.