Study On The Rooting Of The Softwood Cutting Mechanism And Molecular Basis Of Magnolia Wufengensis

Magnolia wufengensis has high ornamental and economic value because of its gorgeous flower color and beautiful flower type,and is a cherished landscaping tree species.However,there are difficulties in breeding.Cuttings,grafting,striping and rooting are the most important ways to carry out asexual reproduction of forest trees at present,among which cuttings have become the most commonly used means of operation because of their good application effect,simple operation,high reproductive coefficient and convenient management.However,the low rooting rate of cuttings is the biggest problem restricting the reproduction of Magnolia wufengensis cuttings.To solve this problem,it is necessary to have an in-depth understanding of the mechanism of rooting of Magnolia wufengensis cuttings,so as to take targeted countermeasures.The rooting of plant cuttings is a complex and changeable biological process,and to understand its rooting mechanism,it is necessary to study it from many aspects.In this study,the regulatory mechanism of rooting of young branches of safflower magnolia was studied from three aspects:physiological biochemistry,transcriptome analysis and endogenous hormone levels.The main results are as follows:1.Using 3 kinds of plant growth regulators NAA,IBA and IAA,each three concentration gradients 500mg/L,1000 mg/L and 1500mg/L,plus water control for a total of 10 groups of treatment,70 days later,statistics of rooting rate,the best treatment sampling for follow-up experiments.Among them,the rooting rate of NAA treatment was higher than that of the other two plant growth regulators.The optimal concentration of NAA treatment was 1000 mg/L,and the rooting rate was 49.3%.2.Physiological and biochemical analysis results showed that there was no significant difference in the content of soluble sugar and soluble protein in fresh untreated cuttings（initial stage S1a）and cuttings treated with plant growth regulators（1000 mg/L NAA）for6 h（initial stage S1b）.,the content of soluble sugar and soluble protein in the cuttings with white protrusions at the base at about 14 days（root primordium formation stage S2）and the cuttings with adventitious roots at about 35 days（adventitious root elongation stage S3）were significantly lower than those in S1 cuttings.During the rooting process of cuttings,there was a significant decrease trend.The superoxide dismutase（SOD）activity in cuttings was the strongest in S1b,and continued to decrease in S2 and S3 stages.The peroxidase（POD）activity in the cuttings was greatly enhanced from S1a to S1b stage,continuously enhanced from S1 to S2,and slightly weakened at S3.The above results indicate that the consumption of soluble sugar and soluble protein contributes to the formation of root primordia and the elongation and growth of adventitious roots in Magnolia wufengensis cuttings.The relatively high SOD enzyme activity was helpful for the survival of cuttings at the initial stage of cuttings,and the enhanced POD enzyme activity promoted the growth and development of adventitious roots.3.Transcriptome sequencing analysis:Each of Magnolia wufengensis cuttings ottained40 million clean raw reads;a total of 186303 Unigenes were assembled,all of which were846nt in length,and the annotation rate exceeded 47.32%（88161）in seven data such as NR,Nt,GG,Swiss-Prot,KEGG,COG and Pfam.Differential expression gene analysis showed that compared with 0h,there were 3205 differentially up-regulated genes and 5248differentially down-regulated genes in 2w;there were 4262 differentially up-regulated genes and 6305 differentially down-regulated genes in 5w,Most of their differentially expressed genes are concentrated in pathways related to plant cuttings,such as hormone metabolites,hormone signal transduction,and sucrose and protein metabolites.Comprehensive KEGG and GO function analysis,in which three differentially expressed genes related to rooting were screened:Cluster-53.109833（Auxin early response gene protein IAA）,Cluster-Cluster-53.31619（Abscisic acid signal transduction pathway upstream receptor protein PYL）,Cluster-53.95403（Negative regulatory protein DELLA in the mycin signal transduction pathway,DELLA）.4.Analysis of endogenous hormone content:Compared with S1b,the concentrations of IAA,ABA,GA₃ and Zeatin in cuttings treated with plant growth regulator NAA all increased significantly;The concentration curve was close to IAA;the concentration of GA₃increased significantly in S2 compared with S1b,and decreased significantly in S3;Zeatin concentration did not change significantly in S2 and S1b,and decreased significantly to the level of S1a in S3.There was no significant difference in the ratio of IAA toABA at S1 stage,but it increased greatly at S2 and decreased slightly at S3.The above results show that the plant growth regulator NAA can significantly change the hormone levels in fresh cuttings of Magnolia wufengensis,and enhance the rooting ability of the cuttings.High concentration of Zeatin is beneficial to the formation of root primordia,but not conducive to adventitious root growth.A high IAA/ABA value is beneficial to the formation of root primordia.Referring to the differentially expressed genes in the transcriptome data,it is inferred that In the process of safflower magnolia cuttings,the expression of the early response gene protein IAA was significantly increased,and the IAA concentration in the cuttings was increased by positive regulation of the IAA signaling pathway,thereby promoting the growth of the cuttings roots;the expression of PYL protein was significantly reduced,and the concentration of ABA in the cuttings was reduced by positive regulation of ABA signal transduction,which weakened the inhibition effect of ABA on rooting,thereby promoting the growth of adventitious roots.DELLA protein expression was significantly reduced,and the GA concentration in the cuttings was increased by negatively regulating GA signal transduction,thereby promoting the undistermined growth of cuttings roots.The above research results have laid a theoretical foundation for further solving the problem of propagation of Magnolia wufengensis cuttings,and can also provide a reference basis for the protection of Magnolia wufengensis resources and large-scale breeding.