Expression Of ERF And NAC Transcription Factors During Postharvest Browning Of Lotus Roots

ERF is one of the largest transcription factor gene families in plants.A large number of studies have shown that ERF is widely involved in the biological and abiotic stress responses of plants,including cold stress,heat stress,hypoxia stress and so on.As the most important element in the ethylene signal transduction pathway,ERF plays a crucial role in the post-harvest quality transcription of fruits and vegetables.NAC transcription factor is a plant-specific transcription factor,which participates in the growth and development of plants and the biological and abiotic stress responses of plants,including cold stress,heat stress,hypoxia stress and so on..Meanwhile,NAC participates in transcriptional regulation during storage of fruits and vegetables.ERF and NAC generally achieve transcriptional regulation through the binding of downstream structural genes.The main reason for the browning of fresh-cut lotus root is enzymatic browning.There have been numerous reports that PAL,PPO and POD are the key enzymes in enzymatic browning of fruits and vegetables.PAL,PPO and POD genes are the target genes forbrowning of fruits and vegetables.In plants,low-temperature storage,modified atmosphere packaging and vacuum packaging are mostly unfavorable abiotic stresses,but for lotus root,it is an effective technique for retarding browning.Therefore,it is a deep research on the molecular mechanism of lotus root browning to explore whether ERF and NAC involved in lotus root browning through transcriptional regulation related genesIn this study,fresh-cut lotus root was taken as test material to analyze the effects of post-harvest appearance,browning degree,total phenolic content,PAL,PPO,and POD activity of lotus root in different varieties under the different storage conditions?low temperature,high concentration of CO₂ and vacuum?by physiological and biochemical methods.The bioinformatics methods and QPCR techniques were used to screen the key PAL,PPO and POD genes for the browning of fresh lotus root.The key elements of ERF and NAC involved in the regulation of PAL,PPO and POD were further screened and their correlation with browning target genes was analyzed.The preliminary identification of the key ERF and NAC genes provides the basis for the study of transcriptional regulation mechanism of lotus root browning.The results of the study are as follows:1.Low temperature?4??,high concentration CO₂,and vacuum all can effectively delay the browning of lotus roots.The activities of PAL,PPO and POD enzymes showed a significant positive correlation with the degree of browning.The possible mechanism was that the activity of browning-related enzymes was reduced under low temperature and hypoxia stress conditions,thereby inhibiting fresh-cut lotus root browning.2.The low temperature inhibited NnPAL1,NnPPOA,NnPOD2-5 expression,but the high concentration CO2 and vacuum inhibited Nn PAL1,Nn PPOA,Nn POD2/3 expression,consistent with the browning process.Therefore,Nn PAL1,Nn PPOA and Nn POD2/3 may be the key target genes for the browning of fresh lotus root.3.Seven Nn ERF and five Nn NAC were isolated from lotus root by RNA-seq and NCBI.Phylogenetic tree analysis found that Nn ERF and Nn NAC shared certain homology with different members of the Arabidopsis gene family.The low temperature inhibited Nn ERF4/5 and Nn NAC1/2/3 expression,but the high concentration CO2 and vacuum inhibited Nn ERF2/5 and Nn NAC1/3/4 expression,consistent with the Browning process.Therefore,Nn ERF5 and Nn NAC1/3 may be key transcriptional regulators of fresh-cut lotus root browning.4.Correlation analysis found that Nn ERF5 expression was highly correlated with Nn PAL1;Nn NAC1 and Nn PPOA were highly correlated,and Nn NAC3 and Nn POD2 were significantly correlated.To participate the metabolism of lotus root and then the browning process of post-harvest lotus root,Nn ERF5 may regulate Nn PAL1,Nn NAC1 may regulate Nn PPOA,while Nn NAC3 may regulate Nn POD2.However,the mutual relationship needs to be further verified.