Functional Analysis Of Arabidopsis MYB55 Transcription Factor And Cotton Sterol

MYB is one of the most important transcription factors in plants with large members and diverse functions.MYB proteins have several MYB domain repeats conferring their ability to bind target genes.As the key factors in regulatory networks,MYB can regulate some plant specific processes,including plant development,metabolism and responses to biotic and abiotic stresses.This study characterized a MYB transcription factor,AtMYB55 in Arabidopsis thaliana and reported its potential function in cellulose biosynthesis and responses to abiotic stresses.Here are major results below:1.Based on protein sequence analysis,AtMYB55 has two DNA-binding domain(MYB domain)repeats,as R2R3-MYB transcription factor.2.AtMYB55 gene has three transcripts in Arabidopsis.Using 3 pairs of primers,it only gets the AtMYB55.1 CDS sequence for overexpression and RNA interference expression vector constructions.T3 generation overexpression homozygous line and T1 generation inhibit-expression line were obtained.3.Compared with the wild type Arabidopsis(Col-0),the overexpression transgenic lines showed a reduced seed germination rate and cotyledon greening under the condition of abscisic acid(ABA),Na Cl and high concentration of sucrose,suggesting that AtMYB55 may be involved in ABA pathway and play an important role in biotic stresses.4.The AtMYB55 overexpressed transgenic lines showed an increased cellulose content and crystallinity with similar expression patters to AtCesA4,AtCesA7 and AtCesA8,suggesting that AtMYB55 may be involved in cellulose biosynthesis.As cotton fibers are important textile materials,understanding of cellulose biosynthesis of cotton fibers becomes scientific signifiance.Althugh it has been reported that sterol glycosides act as a primer cellulose chain elongation in vitro,much remains unknown about function of sterol glucosyltransferase.In this study,w e selected transgenic plants in Arabidopsis and tobacco(Nicotiana benthamiana)by overexpressing cotton sterol glucosyltransferase.Here are major results:1.According to the sequence of GhSGT1 and GhSGT2 that had been cloned in cotton,we constructed overexpression and RNA interference vectors of both genes.2.Both GhSGT1 and GhSGT2 overexpressed transgenic Arabidopsis lines did no exhibited different plant growth phenotypes from wild type.3.Despite of a similar cellulose level,both GhSGT1 and GhSGT2 transgenic Arabidopsis lines showed a reduced degree of polymerization of cellulose,compared with wild type.4.Cellular localization indicated that GhSGT2-EGFP fusion protein mainly accumulated in membrane of tobacco through transient expression assay.