Transcriptomic Profiling Of Taproot Development In Sugar Beet (Beta Vulgaris L.) And The Functional Analysis Of BvDof

In sugar beet(Beta vulgaris L.),taproot weight and sucrose content are the important economic characters.However,high yield leads to low sucrose content when taproot is overweight.Therefore,it is important theoretical basis for increasing the yield and sucrose content of sugar beet taproot that reveal the molecular mechanism of taproot growth and sucrose accumulation.The advances in next-generation sequencing technology and the publication of sugar beet genome have provided a method for the study of molecular mechanism underlying the regulation of these two agronomic traits.In this work,we performed comparative transcriptomic analyses in the high taproot yield cultivar SD13829 and the high sucrose content cultivar BS02 at five developmental stages,using RN A-seq.Transcriptomic profiling was verified via the analyses of endogenous hormone content and anatomical structure,and the functional analysis of core genes in Arabidopsis thaliana.Obtained the following results:1.More than 50,000,000 pair-end clean reads for each c DNA library were generated,and the results of clean read mapping met the requirement of further analyses.There were about 18000 housekeeping genes for each cultivar during all stages.Except the initial stage of taproot growth,the numbers of specifically expressed genes at other stages were relatively constant in both cultivars.2.Via respectively analyses the Differentially expressed genes(DEGs)of the stepwise transcriptome comparisons of two sugar beet cultivars,we found:(1)The DEGs enriched in eighteen gene ontology(GO)terms including,cell wall,cytoskeleton and enzyme linked receptor protein signaling pathway,were involved in regulating taproot turn into raprid growth stage.These genes encode pectinesterase,BGLU,dynein light chain LC8-type,kinesin family member C2/C3,FER,gibberellin-regulated protein 1 and BRI1 et al.(2)KEGG pathway enrichment analysis suggested that brassinosteroid biosynthesis,zeatin biosynthesis,plant hormone signal transduction,phenylpropanoid biosynthesis,ascorbate and aldarate metabolism,and biosynthesis of secondary metabolites pathway were involved in regulating the growth rate of taproot to be rapid(82 DAE)from slow(82 DAE).(3)Some genes involved in plant hornmone signaling,C YP90A1,CYP734A1 and TCH4 et al.,were correlated with regulating the growth rate of taproot to be rapid from slow.The genes involved in zeatin and gibberellin signaling regulated the taproot development at the start stage of rapidly taproot growth.The functional association of genes respectively involved in brassinosteroid and auxin signaling was important for the rapid growth of taproot.SS genes were correlated with the sucrose accumulation of the earlier stage and the taproot growth of the later stage.3.Via respectively analyses the DEGs of the phenotype comparisons at 5 development stages.We found that:(1)The DEGs which were annotated as external encapsulating structure,cell wall and extracellular region terms were correlated with the difference of growth rate between the taproots of two cultivars at the rapid growth stage.And the DEGs which were annotated as cell wall term were also correlated with this difference at the transition stage before focusing in sucrose accumulation.For example,the encoding genes of BGLU and FER.(2)The difference of the activity of plant hormone signal transduction signaling and ascorbate and aldarate metabolism signaling led to the difference of the growth rate between the taproots of two cultivars at the most rapid stage of taproot growth.(3)Some genes involved in plant hornmone signaling,TCH4,C YCD3 and B-ARR et al.,were involved in regulating the growth strategy.Therefore,these genes could improve the growth rate of E-type taproot.4.Starch and sucrose metabolic pathway may correlated with the difference of sucrose accumulation between the taproots of two cultivars at the sluggish growth stage of taproot with still active sucrose accumulation.Analyzing the expression pattern of SPS,SS and SI suggested that the difference of sucrose accumulation between the taproots of two cultivars was correlated with the expression level of SPS and SI at the transition stage(113 DAE)before focusing in sucrose accumulation only.But it was not significantly correlated with the expression level of SPS,SS and SI at other stages.The primary cause for lower sucrose content in the E-type cultivars SD13829 was not caused by enzymes in sucrose metabolism but the rate of cell enlargement that was promoted by brassinosteroid signaling.The weight and sucrose content of taproot relied on its growth strategy.5.The analyses of DEGs suggested that the growth rate of taproot was correlated with the expression level of Bv Dof.The bioinformatics analyses were performed with Bv Dof family.In order to analyze the function of Bv Dof,two members of Bv Dof were cloned and transferred into Arabidopsis thaliana.The results suggested that:(1)A total of 22 Dof family genes were identified in the genome of Beta vulgaris.All of the Bv Dof can be separated into 9 subgroups.There was one tandemly gene duplication event when Bv Dof family is formation.(2)Bv1_zfms,Bv_ofna,Bv5_racn and Bv6_augo may together involved in regulating the development of secondarily cambial.Bv9_nood,Bv1_zfms and Bv6_cdca were correlated with the growth rate of taproot.(3)The overexpression of Bv6_cdca and Bv1_zfms in Arabidopsis thaliana suggested that they activated the expression of At TCH4/At XTH and At BGLU,and suppressed the expression of core cell cycle genes(At CDKB1;1,At CYCA2;1,At CYCA3;1,At CYCB1;1,At CYCB2;1 and At CYCD3;1).Based on this molecular mechanism,Bv6_cdca and Bv1_zfms could improve the cell growth in root,therefore the root length,root weight and root volume of overexpression lines were more than the wild type line.6.The analyses of endogenous plant hormones content and vegetable anatomy suggested that the taproot of E-type cultivar SD13829 had higher zeatin activity,and the growth of parenchymal cell between the rings was more rapid compared to the taproot of Z-type cultivar BS02,at the start stage of rapidly taproot growth.The taproot of E-type cultivar SD13829 had higher BR content when it turn to the rapid growth stage.The enlargement of parenchymal cells in the taproot of E-type cultivar SD13829 was more active than that in Z-type cultivar BS02.But the increase of cell number in the taproot of Z-type cultivar BS02 was more than that in E-type cultivar SD13829.In the taproot of other cultivar,the expression of CYP90A1,BZR1/2,TCH4,CYCD3,YUCCA,B-ARR and Dof which were correlated with the weight increase of taproot shared a similar pattern of the results based on the transcriptome analyses.