The Regulation Mechanism Of The Poplar PtoMYB055 Transcription Factor Involved In Secondary Cell Wall Formation

Poplar is a perennial woody plants. Poplar is one of the main planting tree species in China, the total area had reached more than 12 million hectares. Except for windbreak and sand-fixation, the poplar is widely used in building material and furniture. With the vigorous development of animal husbandry technology, in addition to the trunk, poplar leaf bud, axillary bud, bark, flowers and leaves all can play a key role. For poplar, conventional breeding methods purpose was poor. Studying the previous researches, we want to explore the role of PtoMYB055 transcription factor in secondary wall synthesis regulation. So we can improve the network of poplar secondary wall synthesis and provide a theoretical basis for the optimization of poplar breeding.Sequence analysis of transcription factors PtoMYB055 has showed that the amino acid sequence of PtoMYB055 with R2R3-MYB transcription factors had higher homology. And phylogenetic analysis showed that, compared with other species MYB transcription factors involved in the regulation of secondary cell wall formation, it had a close relationship.The expression of the PtoMYB055 transcription factor was detected in the stem, petiole, phloem and xylem through semi-quantitative and fluorescence quantitative PCR analysis. Consistent with the expression pattern of the PtoMYB055 gene, the results of different organizations showed that the GUS protein most expressed in stem, petiole, phloem and xylem, when poplar was transformed with the promoter of PtoMYB055.As a transcription factor, PtoMYB055 protein is localizated in the nucleus on the basis of subcellular localization. The experiment of yeast one-hybrid assay also proved that PtoMYB055 had transcription activation, as activation of transcription factor.When poplar transformation with PtoMYB055 by Agrobacterium-mediated leaf disc method, PtoMYB055-overexpression transgenic poplar was got. Compared with wild type plants, PtoMYB055-overexpression plants were more dwarf and had curl leaves. The measure of leaf area, plant height and diameter all decreased significantly. Compared with wide type poplar, the PtaMYB055-overexpression plants had much more ectopic deposition of lignin. Lignin autofluorescence under UV light also showed similar results. The content of lignin in transgenic plants increased significantly by the measurement of Klason method.Interestingly, comparing with wide type poplar, lignin ectopic deposition was clearly observed in early young leaf veins of transgenic poplar.However, there was no obvious difference in the mature leaves.The overexpression plants had much more lignin accumulation in vein. The expression levels of key enzyme genes in the secondary wall synthesis showed higher expression level, including C4H4、 CAD1、CCOAOMT1、CCR2、F5H2、COMT2、C3H3、PAL4、CL5、GT43B、GT43D、 CESA2B and CESA3A, when detected them by fluorescence quantitative PCR in transgenic plants. CCR2, CCOAOMT1, CESA2 and GT43B were chosen for further research in the experiment of transactivation analysis. By the method of instantaneous injection infect tobacco, GUS protein activity increased significantly by the activation of PtoMYB055.Above all, PtoMYB055, as a transcription activator, regulated the second cell wall synthesis by activating the expression of key enzyme genes in lignin biosynthetic pathway.