Regulatory Mechanism Of Abscisic Acid On Inducing Wound Suberization In Tomato And Kiwifruit

Fruit are susceptible to physical injury causing postharvest deterioration during harvest,transportation and storage.Quick suberization is an essentially protective callus process for injured fruit to reduce water loss and avoid infecting,playing an important role in maintaining the postharvest quality and shelf-life of injured fruit.The focus of this work was to explore the effect and regulatory mechanism of exogenous abscisic acid(ABA)on wound suberization in postharvest tomato and kiwifruit.1.ABA induced differential expression of genes involved in wound suberization in postharvest tomato(Solanum lycopersicum)fruit.The suberization process with the accumulation of suberin polyphenolics(SPP)and polyaliphatics(SPA)observed through microscopy was accelerated by ABA on the surface of wounded tomato tissue.Expression levels of SlPAL5 and S14CL involved in the synthesis of SPP reached the highest at 4 and 8 day(d)after wounding,respectively,and more increment following ABA application.Associated with SPA biosynthesis,SlLACS1 and SlLACS2 showed the most abundant transcript levels at 8 and 6 d in ABA group,respectively.Transcript levels of other important related enzymes including SlKCS,SICYP86B1,SIFAR3 and SIGPAT were up-regulated at 2 d after wounding by ABA.Enzymatic activities and genes expression of PPO and LOX were also enhanced during wound suberization following ABA application.The results in this chapter proved that ABA accelerated the wound suberization progress and increased the transcript levels of relevant genes in postharvest tomato fruit.2.The wound-healing of postharvest kiwifruit(Actinidia deliciosa)was investigated.The developing period of suberization demonstrated by microscopic observation was 2—4 days after wounding in kiwifruit.Enzymatic activities of PAL,CAD and POD in wound-suberized tissue were enhanced by ABA.The constituent analysis of suberin including SPP and SPA proved that exogenous ABA increased the contents of total phenols,total flavonoids,alkanes,alkenes,alcohols,alkane acids,olefine acids,esters,glycerides and vitamin E in wound-healing tissue.So,it was suggested that ABA stimulated to increase the accumulation of suberin components,further to accelerate healing of wounded kiwifruit.3.The proteomic change induced by ABA in suberized kiwifruit tissues was analyzed.By performing comparative quantitative proteomics based on iTRAQ technique in wound-suberized tissue of kiwifruit,a total of 95 protein species consistently showed differential abundance between ABA and sterile water treatment,including 29 down-regulated and 66 up-regulated protein species.The KEGG and protein-protein interaction analyses revealed that ABA mainly affected the antioxidant system,phenylpropanoid metabolism and lipid metabolism.Based on proteomics analysis,the similarly differential expression of genes encoding differential abundance protein species was also confirmed by qRT-PCR analysis.Considering the above results,GSH-Px,MDHAR,SOD,APX and POD of antioxidant system,PAL,CCR and PPO of phenylpropanoid metabolism,CYP86B1,DGGT and KCS11 of lipid metabolism,were regarded as the key enzymes in the response of ABA during wound suberization.4.The molecular mechanism by which ABA regulates suberization induced by wounding was explored.During wound suberization of kiwifruit,the transcript level of Achn030011(designated as AchnKCS),a member of ?-ketoacyl-coenzyme A synthases(KCSs)family,was significantly upregulated by ABA.And the subcellular localization of AchnKCS was in the endoplasmic reticulum(ER).Five transcription factors(Achn340751,Achn270881,Achn025721,Achn091781 and Achn117821)were screened through promoter analysis of AchnKCS.They were designated as AchnbZIP29,AchnbZIP12,AchnbZIP2,AchnbZIP62 and AchnMYB70,respectively,according to their homology with Arabidopsis transcription factors.Yeast one-hybrid and double luciferase assays demonstrated the significant trans-activation of AchnbZIP 12 and AchnMYB70 on AchnKCS promoter.However,AchnbZIP29 displayed the inhibitory effect on AchnKCS promoter.Further study showed the transcript levels of AchnbZIPl2 and AchnMYB70 were upregulated by ABA,which was synchronously with the change of transcript abundance of AchnKCS during wound suberization.Conversely,there had a decreased effect on AchnbZIP29 transcript level by ABA.This chapter illustrated that AchnbZIP12 and AchnMYB70 played important roles in the ABA-mediated AchnKCS transcription during wound suberization of kiwifruit.