The Transcription Factor PtoMYB115 Contributes To The Regulation Of Proanthocyanidin Biosynthesis And Enhances Fungal Resistance In Poplar

Poplar is a widespread forest tree with significant economic and ecological importance worldwide.In the natural environment,poplars are stressed by different kinds of fungus diseases,one of the most destructive diseases of poplar is Dothiorella gregaria Sacc,which causes premature leaf drop,loss of biomass and vigor,and even death in poplar plantations.Plants produce a variety of secondary metabolites,condensed tannin also called proanthocyanidin is a kind of secondary metabolites in plant flavonoids metabolic pathways.Condensed tannin are also constitutively produced in poplar leaves,but their biosynt hesis is often up-regulated by stresses such as insect herbivory,mechanical wounding,and pathogen infection.Therefore condensed tannin is a kind of secondary metabolites against various stresses and produced in the process of long time adapt to the natural environment.According to VvMYBPA1 amino acid sequence,we BLAST homologous MYB transcription factors in poplar.We have cloned PtoMYB115 full-length cDNA,sequence comparison of the PtoMYB115 with other known R2R3-MYB proteins of regulating flavonoid metabolism.We found PtoMYB115 reveals high amino acid sequence similarity with other R2R3-MYBs,and the R2R3 DNA-binding domain of PtoMYB115 is most closely related to VvMYBPA1 and DkMYB4,which are MYB transcription factors involved in proanthocyanidin biosynthesis.The PtoMYB115 was high expression and proanthocyanidin concentration found increase significantly after mechanical wounding,infecting Dothiorella gregaria Sacc.,and exposure to elevated high light to treat wild type P.tomentosa Carr.We isolated the promoter 1432bp sequence of PtoMYB115,analysis revealed several abiotic stress-responsive cis-regulator elements.Subcellular localization and transcriptional activation analysis showed PtoMYB115 was exclusively localized in the nucleus and PtoMYB115 is a transcriptional activator.To determine PtoMYB115 function,PtoMYB115 was overexpressed in transgenic P.tomentosa Carr.plants via Agrobacterium mediation.A significantly higher accumulation of proanthocyanidin was detected in transgenic plants compared to the wild-type control.We found PtoMYB115 up-regulate the expression levels of some structural genes of the proanthocyanidin biosynthetic pathway.The PtoMYB115 interaction with bHLH-like protein and WD40-like protein could activate the structure genes of promoters.In vitro assays showed that the transgenic poplar plants displayed a significant reduction in their plaque area compared with the control.These results suggested that PtoMYB115 is specific to regulation of PA biosynthesis in poplar and improve the plant disease resistance.