Functional Analysis Of PtrBTB70 In Wood Formation Of Populus Trichocarpa

Wood is a widely abundant biomass produced by plants,and plays a crucial role in reducing carbon dioxide levels in the atmosphere.Wood formation is a complex developmental process that involves several stages,including cambial cell proliferation,xylem cell expansion,secondary wall deposition,and programmed cell death.In previous studies,many genes involved in wood formation have been identified,but the functions of several genes remain unknown.BTB/POZ protein family members are widely distributed in plants.Different BTB protein subfamily members play different functions,including regulating the growth and development of plants,resisting the invasion of pathogens,participating in the metabolic process of plants and responding to abiotic stress.However,the function of BTB proteins in wood formation has not been well explored.In this study,the function of PtrBTB70 in the secondary cell wall development of Populus trichocarpa was analyzed.The main results are as follows:A total of 87 BTB protein family members were identified in the Populus trichocarpa genome through a blast search of the Populus trichocarpa database,and they were named PtrBTB1-PtrBTB87 based on their position on the chromosome.Electronic expression data showed that the PtrBTB70 had the highest expression level in the xylem,so this gene was selected as the research object.PtrBTB70 of Populus trichocarpa has a total c DNA sequence of 819 bp,encodes a protein with 273 amino acids,and contains a BTB domain and a BACK domain.Through transient transformation experiments in tobacco leaf epidermal cells,it was found that PtrBTB70 was located on the cell membrane.The transcriptional activity of PtrBTB70 was analyzed by yeast self-activation experiments,and it was found that PtrBTB70 had no self-activation activity.The expression of the PtrBTB70 in different tissues of Populus trichocarpa was analyzed by RT-PCR and q RT-PCR.The results showed that PtrBTB70 was highly expressed in the xylem of Populus trichocarpa.The promoter sequence of PtrBTB70 was analyzed,and it was found that the promoter region contained the secondary growth dependent cis-acting elements M46 RE,SMRE1 and AC-I,suggesting that its function might be related to wood development.The plant over-expression vector of p CAMBIA1300-35S::PtrBTB70-3×flag was construc-ed and genetically transformed into Populus trichocarpa by agrobacterium transformation.Six PtrBTB70 overexpression transgenic lines were obtained and identified at the DNA and RNA levels.Phenotypic observation showed that the plant height of the over-expressed plants increased and the stem node diameter decreased compared with the wild type.The section staining and component content determination indicated that the excessive expression of PtrBTB70 lead to an increase in lignin content and a decrease in cellulose content of the transgenic lines.Observation of samples under the scanning electron microscope indicated that the excessive expression of PtrBTB70 decreased the width of the xylem of Populus trichocarpa,reduced the size of fiber cells,and did not affect the thickness of mature Xylem cell wall.In conclusion,PtrBTB70 may affect the development and formation of wood by affecting the deposition of cellulose and lignin in the xylem of Populus trichocarpa.