Function Of Poplar Transcription Factor PtoMYB48 In Regulation Of Secondary Wall Synthesis

Poplar is the main afforestation tree species in our country.Because of its easy cultivation,strong adaptability,and fast growth,it is of great significance to wind prevention,sand fixation and desert greening.Meanwhile,poplar is also an important timber resource,which is widely used in the construction,paper and breeding industry.Due to these characteristics,poplar has always been the focus of research on genetics and breeding of forest trees in my country.As one of the main components of plant stems,wood is an important source of renewable bioenergy.Themost important component of it is the secondary cell wall.The secondary cell wall plays a essential role in the growth,development and disease resistanceof plant.At present,the research of poplar species has moved from conventional breeding to genetically modified breeding.A large number of poplars whose internal genes have been modified genetically have shown excellent characteristics,especially those whose wood composition and content have been changed.It brings great economic benefits and promotes the elucidation of the synthetic network of secondary walls in wood.With the completion of the whole genome sequencing of Populus tomentosa,Populus euphratica and Populus euphratica,genetic transformation and regeneration systems of various poplars have been established in recent years,and poplars have become the most useful model system for the study of woodyplants.Lignin is the main component of the secondary wall,and the biosynthesis of lignin is through the phenylpropane metabolic pathway.This pathway uses phenylalanine and tyrosine as substrates,catalyzing by phenylalanine lyase,cinnamic acid-4 hydroxylase,and etc.In the early stage,through transcriptome analysis of the Arabidopsis mutant wat1 with defects in xylem synthesis,we found a set of transcription factors with significant expression differences(AT3G46130,AT1G17950,AT3G11280.1),and speculated that they may be involved in the secondary wall synthesis.In this research,we foucus on PtoMYB48 of Populus tomentosa,which is the homologous gene of AT3G46130.We studied on its function in the secondary wall biosynthesis and its mechanism of regulation.The main results are as follows:1.PtoMYB48 is a transcriptional activator and locatesin the nucleus Tissue-specific analysis of multiple genes that may affect the biosynthesis of the secondary wall showed that PtoMYB48 was high expressed t in the stem.Subcellular localization and transcriptional activation experiments have confirmed that PtoMYB48 is a transcriptional activator and locates in the nucleus.2.Overexpression of PtoMYB48 promotes secondary wall synthesisPtoMYB48 was overexpressed in Populus tomentosa,and the transgenic plants were screened and comfirmedby PCR amplification,q RT-PCR,and Western Blot.Compared with wild-type,the transgenic platnts were shorter and the internodes of them became shorter.Phloroglucinol and toluidine blue staining showed that,compared with the wild type,the lignin content of the PtoMYB48 overexpression plants were significantly increased,and the secondary wall were thickened;the lignin autofluorescence test results showed that,The autofluorescence loop of the transgenic is significantly wider than that of wild-type plants.This result also confirmed that overexpression of PtoMYB48 can cause an increase in lignin content,and promote the synthesis of the secondary walls.3.PtoMYB48 promotes lignin biosynthesis by up-regulating key enzyme genes in the phenylpropane metabolic pathwayTranscriptome analysis of the PtoMYB48 transgenic and wild-type pnat showed that,there were a total of 2841 differentially expressed genes,including 974up-regulated genes and 1867 down-regulated genes.A targeted analysis of the KEGG annotation results of differentially expressed genes showed that many key regulatory genes in the phenylpropane synthesis pathway were up-regulated in the transgenic plant,such as PAL,4CL,COMT,F5 H,etc.The above results show that,as a transcriptional activator,PtoMYB48 plays a positive regulatory role in the biosynthesis of the secondary wall of Populus tomentosa,and it is very likely to promote the synthesis of lignin by up-regulating some key enzyme genes in the phenylpropane metabolic pathway,and promotesthe secondary wall biosynthesis.