Molecular Mechanism Of Udp-glucose Dehydrogenase Regulate Vegetative Growth In Plants

Dahurian larch,Larix gmelinii(Rupr.),a deciduous tree of the Pinaceae,and genus larch,grows mainly in northeast China,L.gmelinii has extensive application in Civil engineering,building and chemical fiber industry owing to its high-quality timber.UDP-glucose dehydrogenase(UGDH)is a key enzyme in the polysaccharide metabolism pathway of plants,that catalyzes the dehydrogenation of UDP-Glc to UDP-glucuronide(UDP-GlcA),UDP-d-glucuronic acid(UDP-GlcA)is the biosynthetic precursor substance of hemicellulose,and plays a very important role in plant growth and the formation of forest materials.Our previous study has confirmed that LgUGDH not only increased the hemicellulose content in plants,but also significantly promoted its vegetative growth.Moreover,the over-expression of LgUGDH gene significantly improved the cold tolerance of plants.Therefore,the study on expression regulation mechanism of the LgUGDH gene has important significance.Southern blot analysis indicated that LgUGDH is encoded by two paralogous genes in L.gmelinii.Real-time fluorescent quantitative-PCR analysis showed that the LgUGDH1/2 expressed in the roots,stems,and leaves of the larch.In this study,for analyzing the expression characteristics of LgUGDH1/2,a 1352-bp of LgUGDH1 gene promoter sequence was cloned by chromosome walking,and was analyzed by comparing with the promoter sequence of LgUGDH2 isolated in our previous study.The PLANTCARE analysis showed that pLgUGDH1/2 contains photoinducible elements and abiotic-stress response elements such as low temperature,but also the hormone-responsive elementsincluding abscisic acid,gibberellin,methyl and jasmonateauxin.GUS staining experiments indicated that the pLgUGDH1::GUS expressed in the cotyledons,roots,mature leaves,flowers and pods of Arabidopsis;pLgUGDH2::GUS majorly expressed in the leaf veins,cotyledons,lowers and pods of Arabidopsis.And its expression is induced by ABA and low temperature.The subcellular localization of LgUGDH1 showed that the LgUGDH1-GFP fusion protein was localized in the chloroplast.The phenotype analysis of wild-typ,atugp1 mutant,atugp1 functional complement lines and LgUGDH-overexpressing lines were analyzed,The results showed that overexpression of the LgUGDH increased the content of hemicellulose,lignin and soluble sugarin transgenic Arabidopsis thaliana,promoted the vegetative growth of transgenic Arabidopsis.For further studying the mechanism of LgUGDH gene promoting vegetative growth of transgenic Arabidopsis thaliana,the transcriptome of wild type,atugdh1 mutants and overexpressed LgUGDH transgenic Arabidopsis thaliana were analyzed.The differentially expressed genes were annotated into starch and sucrose metabolism,phenylpropane biosynthesis,carbon metabolism,photosynthesis,plant-pathogen interactions,and plant hormone signal transduction pathways.Therefore,it is speculated that UGDH may regulate growth and development and adaptation to adversity of plant through carbon metabolism,glucose metabolism,phenylpropane metabolism,plant-pathogen interaction and plant hormone signal transduction.These results lay a foundation for analyzing the growth and development of plant regulated by glucose dehydrogenase(UGDH)through polysaccharide metabolism.This study also provides experimental basis for analyzing the functional mechanism and expression regulation of LgUGDH gene,as well as genetic breeding of forest trees by using LgUGDH.