Study On Semi-lignified Cutting Technique And Molecular Mechanism Of Rooting Of Mei In Beijing

Mei（Prunus mume Sieb.Et Zucc.）is a traditional flower in China.The differences in rooting of Mei cultivars affect its popularization and application.We compared the rooting ability of different cultivars of Mei and screened suitable exogenous hormones for cuttings.Using the morphological anatomy and comparative transcriptomics research in the key period of rooting,exploring the molecular mechanism of the adventitious root（AR）formation of semi-lignified cuttings can provide a basis for the research and practical application of Mei cutting propagation.The main results and conclusions are as follows:The semi-lignified cutting propagation technique of Mei was studied in this work,the results showed that,（1）The cuttings of P.mume‘Xiangxue Gongfen’,P.mume‘Jiangsha Gongfen’,P.mume‘Zhusha Wanzhaoshui’,P.mume‘Jiangnan’,P.mume‘Zao Yudie’,P.mume‘Fei lve’,P.mume‘Fenhong Zhusha’and P.mume‘Wu Yuyu’were treated with 2000 mg·L^-1 IBA for eight seconds.P.mume‘Fenhong Zhusha’,P.mume‘Jiangsha Gongfen’and P.mume‘Xiangxue Gongfen’are more suitable with this treatment.（2）The semi-lignified cuttings of P.mume‘Fenhong Zhusha’and P.mume‘Wu Yuyu’were treated with single hormone and compound hormone respectively.It was found that P.mume‘Fenhong Zhusha’was easier to root than P.mume‘Wu Yuyu’.The treatment with 2000 mg·L^-1 IBA for eight seconds of two cultivars had the best effect.The survival rate,callus formation rate,rooting rate and rooting index of P.mume‘Fenhong Zhusha’were 51.67%,31.67%,30.00%and 3.57 cm,respectively.While the same indexes of P.mume‘Wu Yuyu’were 48.33%,30%,10%and 0.79 cm,respectively.These treatment of melatonin(0.23～4.64 mg·L^-1 for eight seconds)are not suitable for rooting of the two cultivars of Mei.By observing the rooting situation of 8 cultivars,it was found that cutting at the end of August belonged to mixed rooting type.Morphological and anatomical observations of the AR formation process of the cuttings of P.mume‘Xiangxue Gongfen’and P.mume‘Zhusha Wanzhaoshui’found that the annual stems of the two cultivars were in the secondary growth stage,and there was no latent root primordium in the stems at the end of August.The two cultivars belonged to the induced rooting type,and the ARs occurred in multiple sites:parenchyma cells at the intersection of cambium and medullary ray,phloem parenchyma cells and callus.Transcriptome sequencing analysis was performed on the four stages of AR formation（initial stage,callus stage,root primordium stage,and AR formation stage）of P.mume‘Xiangxue Gongfen’and P.mume‘Zhusha Wanzhaoshui’cuttings by Illumina Hiseq 2500.The results are as follows,（1）A total of44.1768～67.2238 million clean reads were obtained,and the number of effective bases was 6.58-10.03Gb,and total 25094 genes were identified by comparing the reference genome of Mei.There were more differentially expressed genes（DEGs）during the callus formation period and AR formation period of the two cultivars,and more co-expressed genes during the callus formation period.It is suggested that the callus formation period may be the key period for the formation of ARs of Mei cuttings.The most DEGs at the stage of AR formation may be the main reason for the difference in rooting ability between P.mume‘Xiangxue Gongfen’and P.mume‘Zhusha Wanzhaoshui’.（2）GO and KEGG enrichment analysis were performed on the DEGs in each group.During the formation of ARs of Mei cuttings,the up-regulated differentially co-expressed genes during callus formation were significantly enriched in pathways such as glutathione metabolism,cell cycle,secondary metab olite biosynthesis,and pheny lpropane biosynthesis.The down-regulated differentially co-expressed genes were significantly enriched in the pathways of photosynthesis,glyox ylic acid and dicarboxylic acid metabolism,andα-linolenic acid metabolism.P.mume‘Xiangxue Gongfen’compared with P.mume‘Zhusha Wanzhaoshui’,in the AR formation stage,differentially expressed genes were significantly enriched in phenylpropane biosynthesis,secondary metabolite biosynthesis,flavonoid biosynthesis,plant-pathogen interaction,brassinolide biosynthesis and other pathways.（3）By analyzing the expression patterns of genes related to photosynthesis,sugar metabolism,plant hormone synthesis and signal transduction,cell cycle and AR development during the formation of Mei ARs,combined with the morphological and anatomical observation of AR formation of cuttings,it was found that YUC10,CYCD3-2,CYCD3-3,LRP1,LBD16,LBD18,LBD29,etc.may be related to the rooting of Mei semi-lignified cuttings.