Study On The Role Of Abscisic Acid In Postharvest Physiological Deterioration Of Cassava And Its Regulation Of Antioxidant System

Cassava（Manihot esculenta Crantz）is one of the most important economic crops in tropical and subtropical area,representing the staple security for more than one billion of people.However,the sustainable development of cassava industry was seriously restricted by postharvest physiological deterioration（PPD）which occurs within 72 hours following harvest.Numerious studies have proved that plant hormones and signaling molecules play important roles in regulating postharvest physiological deterioration of cassava.However,the role of abscisic acid（ABA）in post-harvest physiological deterioration of cassava and its regulatory mechanism are unclear.In this study,physiological and biochemical techniques,such as yeast two hybrid,yeast one hybrid and in vivo co-expression,were used to study the regulatory effect of exogenous ABA treatment on cassava postharvest physiological deterioration.In addition,the interaction and co-expression of core components in ABA signaling pathway were analysed,and the effects of MebZIP5 and meb ZIP34,transcription factors in ABA pathway,on the antioxidant system mediated by glutaredoxin（GRX）and monodehydroascorbate reductase（MDAR）respectively were identified.This study preliminary revealed the molecular mechanism of ABA in delaying cassava postharvest physiological deterioration,which provided a scientific basis for the effective control of cassava postharvest physiological deterioration,The main results are as follows:1.The regulation effect of exogenous ABA treatment on PPD of cassava,100μmol/L,300μmol/L,and 500μmol/L ABA were used to treat cassava cultivar“SC8”storage roots respectively.It was found that 300μmol/L and 500μmol/L ABA can significantly delay PPD.Besides,treating the storage roots of the other four cassava varieties（KU50,SC9,SC205,SM）with 300μmol/L ABA can also significantly delay PPD.Exogenous ABA treatment resulted in a significant increase in the content of endogenous ABA content and a significant decrease in the hydrogen peroxide（H₂O₂）content during the PPD of cassava.2.Based on previous transcriptome data,14 ABA signaling pathway members（including 4 Me PYLs,5 clade A Me PP2Cs,3 Me Sn RK2s,2 clade A MebZIPs）were screened and cloned.Through yeast two hybrid and Bimolecular fluorescence complementation（Bi FC）experiments,it was found that Me PYL6 and Me PP2C16,Me PP2C16 and Me Sn RK2.2/2.4,Me Sn RK2.2 and MebZIP34,Me Sn RK2.4 and MebZIP5/34 had interactions,respectively.Expression analysis showed that these genes were induced by ABA during the process of PPD of cassava.Determining the interaction relationship of core components of the ABA signaling pathway and co-expression regulation mode:3.In the ABA pathway,transcription factors MebZIP5 and MebZIP34 regulate Me GRX6 and Me MDAR1 to mediate the antioxidant system,Based on previous transcriptome data,the expression level of 15 antioxidant system-related genes were found to increase expression level significantly during PPD,and their promoter contained ABRE elements that may interact with clade A b ZIP members.The interaction of MebZIP5 and MebZIP34 with the promoter of Me GRX6 and Me MDAR1 were confirmed both by yeast one hybrid and dual luciferase experiments.In addition,the analysis of expression pattern and enzyme activity showed that both the expression level and enzyme activity of Me GRX6 and Me MDAR1 were significantly induced by ABA during the PPD process of cassava;In addition,it is found that other antioxidant indexes POD,CAT,VC,and GSH activity were induced by ABA during the PPD process of cassava.In summary,the results of this study preliminary revealed that ABA regulate the expression level and enzyme activity of Me GRX6 and Me MDAR1 through the Me PYL6-Me PP2C16-Me Sn RK2.2/2.4-MebZIP5/34 signal module,leading to the reduce of intracellular H₂O₂level,and thus delay the PPD of cassava storage roots.The research results can provide scientific basis for controlling PPD of cassava,and provide potential genes for genetic improvement of cassava PPD resistance.