Functional Analysis Of LBD21-31 Gene In Stem Secondary Growth Of Populus

Wood resources are of indispensable significance for the entire human society.Wood is indispensable as an energy source for combustion and in paper and construction.Most of the biomass of trees is wood,wood is also called secondary xylem.The vascular cambium cells divide and differentiate inwardly to produce secondary xylem,and outwardly to produce secondary phloem.Following a series of complex development processes such as cell expansion,secondary wall deposition,and programmed cell death make the trunk is thickened.Therefore,studying the genetic regulatory network of secondary growth has important scientific value.In this study,the LBD21-31(Potri.010G186000)gene in the LBD gene family was selected as the research object by analyzing the previous gene expression data,using hybrid poplar 84 K as experimental material,the LBD21-31 gene fragment of poplar was cloned,successfully constructed 35 S :: LBD21-31 overexpression vector,and LBD21-31 overexpressing transgenic plants were infected with Agrobacterium-mediated leaf disc infection transformation technology.The expression of LBD21-31 in different transgenic plants was further detected by RT-qPCR.The effects of LBD21-31 on the callus development,root development and secondary xylem development of poplar were analyzed by phenotypic analysis and plant stem section observation.The target genes related to LBD21-31 were analyzed by DAP-seq.It provides an important theoretical basis for the study of LBD gene family and the selection of poplar varieties.The main research results are as follows:(1)The expression level of LBD21-31 in the secondary xylem is significantly higher than that in the secondary phloem.(2)With reference to the LBD21-31 gene sequence of Populus trichocarpa,the CDS sequence of LBD21-31 was successfully cloned from the 84 K poplar genome.Its CDS is 492 bp in length,with a base sequence similarity of 98.2% and a 100% amino acid sequence similarity.(3)The 35S:: LBD21-31 overexpression vector was successfully constructed,and 35 S :: LBD21-31 overexpression transgenic plants were obtained using Agrobacterium infection technology.(4)Analysis of gene expression of transgenic plants by RT-qPCR showed that transgenic plants with high LBD21-31 expression significantly decreased in height and stem thickness,and defects in xylem development.(5)LBD21-31 over-expressing plant callus excessive proliferation,plant rooting difficulties.(6)Exogenous auxin and cytokinin treatment inhibit LBD21-31 gene expression.(7)1637 target genes directly binding to LBD21-31 were found by DAP-seq,these include NAC transcription factors,MYB transcription factors,and auxin synthesis,transport,and response related factors.