Physiological And Biochemical Responses And Transcriptome Analysis Of Root Development Of Quercus Variabilis Seedlings Induced By Root Cutting

Afforestation is an effective method for forest restoration.In the process of afforestation,in order to facilitate the transplanting and transportation of seedlings,root pruning is usually carried out.However,excessive root pruning has a negative impact on the growth and survival of seedlings,which directly affects the quality of seedlings and afforestation effect.Quercus variabilis is a common tree species used for vegetation construction.In seedling stage,the main roots grow fast,but the lateral fibrous roots are few.In the process of transplanting,the influence mechanism of root cutting on root formation is not clear.In order to further study the internal regulation mechanism of the response strategy of Quercus variabilis seedling root to root cutting injury,the changes of root morphological characteristics and endogenous hormone content of one-year-old potted Quercus variabilis seedling root at different levels and different development stages of normal root(uncut root,CL)and cut root(truncated by 1/3 length of main root,TL)were measured by sand culture method.At the same time,from the level of transcriptomics,the genes that affect the root development of Quercus variabilis seedlings were screened,and the key genes and enzymes that regulate the root development of Quercus variabilis seedlings were determined through biological information analysis,thus clarifying the response mechanism of the root system of Quercus variabilis seedlings to root cutting injury.The main results are as follows:(1)Reasonable root cutting promotes the development of lateral roots in Quercus variabilis Seedlings.With the growth and repair of root system,TL significantly increased the total root length,root surface area,root volume,root tip number,root biomass and root biomass ratio in root system compared with CL group.(2)Thirty-seven compounds of eight kinds of plant hormones were detected by ultra performance liquid chromatography-tandem mass spectrometry(LC-MS/MS).Changes of main endogenous hormones in roots: Root cutting significantly induced the increase of abscisic acid(ABA),jasmonic acid(JA),salicylic acid(SA),ethylene precursor(ACC)and gibberellin(GA3)in roots of Quercus variabilis in the new lateral root induction period,and significantly decreased the content of indole-3-acetic acid(IAA);Starting and producing period of new lateral roots: Compared with CL group,the contents of IAA,5-deoxypterygium alcohol(5DS)and ACC in TL group were significantly increased,while the contents of zeatin nucleoside(ZR)were significantly decreased;New lateral root elongation period: ABA,JA and SA contents in TL group decreased,but IAA content reached the peak.After root cutting,the IAA/ABA value gradually increased,and the IAA/ZR value first decreased and then increased.(3)Correlation analysis showed that IAA content in TL group was positively correlated with total root length,root surface area,root volume,primary lateral root number and root biomass morphological indexes.The contents of ABA,SA and JA hormones in TL group were negatively correlated with total root length,root surface area,root volume,root tip number,root biomass ratio and root biomass,but these indexes were not significantly correlated in CL group.(4)The transcriptome sequencing was used to compare the gene expression of the root-cutting group and the control group.The results showed that there were 3049,3788 and 1919 genes differentially expressed in the three development stages of the new lateral root,respectively.Through correlation analysis,the correlation coefficient of |r|>0.8 between 3498 common DEGs and plant hormone compounds was screened out,and the related number of jasmonic acid-phenylalanine(JA-Phe,1255)was the most,followed by 6-furfuryl aminopurine(K,589),indoleacetic acid-valine(IAA-Val,214),indoleacetic acid-glycine(IAA-Glu,139),ABA(103),gibberellin7(GA7,52),etc.A total of 20 DEGs strongly related to the corresponding hormone compounds were enriched into the KEGG pathways related to plant hormone synthesis and signal transduction.(5)By transcriptomics in combination with LC-MS/MS analysis,The key genes that may promote root development and stress regulation of Quercus variabilis seedlings were screened out: auxin-induced root culture protein(Cluster-67598.50456),auxin responsive protein(Cluster-67598.65012),zinc finger protein(Cluster-67598.34088),Acyl-Co A oxidase(Cluster-67598.17226)and hydroperoxide dehydratase(Cluster-67598.41882)related to jasmonic acid synthesis;Cytokinin synthesis-related cis-zein O-glucosyltransferase(Cluster-67598.45311)and UDP-glucosyltransferase73C(Cluster-67598.34011),auxin response factor ARF(Cluster-67598.92186),auxin response factor GH3(Cluster-67598.80953),jasmonic acid transcription factor MYC2(Cluster-67598.71502)and SAUR family protein(Cluster-67598.68524).