Functional Analysis Of BvBZR1 Gene In Regulating Taproot Development In Sugar Beet(Beta Vulgaris L.)

Sugar beet(Beta vulgaris L.),a kind of cash crop,is cultivated for obtaining taproot.The growth of taproot is directly related to the yield.Brassinosteroids(BR),as the sixth plant hormone,are involved in regulating a series process of growth and development in plant roots.In this study,paraffin sectioning technique was used to demonstrate the influence of brassinolide in transverse taproot development.Bioinformatics and qPCR were used to identify the transcription factor BZR family genes in the brassinosteroids signaling pathway and their expression patterns.BvBZR1 was overexpressed in sugar beet to demonstrate its biological function in the taproot development.Transcriptome analysis and yeast one-hybrid were used to preliminarily analyze the regulation mechanism of BvBZR1 in taproot development.The main results are Obtained as following:1.Analysis of morphological and structural characteristics showed that BR increase the spacing between cambial rings through promoting the size of parenchyma cells between cambial rings,and eventually resulting in an increase of taproot diameter and weight.2.Through an analysis of the BES1?N conserved domain,six BvBZR family members were identified in the sugar beet genome,and clustered into three subgroups by phylogenetic analysis.Chromosomal mapping analysis showed that,2,1,1,1,and 1BvBZR members were located on chromosomes 1,4,5,6,and 8,respectively.The cis-acting elements related to taproot growth were randomly distributed in the promoter of the BvBZR.The q PCR analysis showed that BvBZRs were all related to the growth of taproot.Tissue-specific expression analyses indicated that all BvBZRs were expressed in three major tissue types(roots,stems,and leaves),with significantly higher expression in leaves.3.Overexpression of BvBZR1 in sugar beet enhanced taproot weight and diameter.4.The transcriptomic topGO analysis of transgenic sugar beet overexpressing BvBZR1 showed that DEGs enriched in growth,development GO terms,including“plant-type cell wall”,“xyloglucan metabolic process”,“xyloglucan: xyloglucosy1 transferase activity”.KEGG pathway enrichment analysis showed that DEGs enriched in “starch and sucrose metabolism”,“glycolysis/gluconeogenesis”.Yeast one-hybrid assay indicated that BvBZR1 could directly bound to the “CACGTG” sequence of BvXTH promoter and “CATGTG” sequence of BvCESA promoter to regulate the expression of BvXTH and BvCESA.5.Overexpression of BvBZR1 in sugar beet promote the BvCESA6?BvXTH33 expression levels and CESA,XTH activities,reduce the BvCEL1 expression level and CEL activity in parenchyma cells between cambial rings which could be beneficial to increase the root diameter and yield.At the same time,Overexpression of BvBZR1 in sugar beet enhance the BvSPS expression level and SPS activity which could increase the sucrose content in taproot.