Studies On The Lateral Organ Boundaries Domain(LBD) Gene Family In Eucalyptus Grandis,Populus Trichocarpa And Gossypium Raimondii

The research of transcription factor families are major focus on functional genomic.In plants,the transcription factor families have been involved in the regulation of many important biological processes,including morphogenesis,signal transduction and environmental stress responses.LBD?Lateral Organ Boundaries Domain?/ASL?ASYMMETRIC LEAVES2-LIKE?proteins are a kind of plant-specific transcription factor,which play key roles in the regulation of plant growth and development,nutrition metabolism as well as response to adversity stress.Eucalyptus grandis and Populus trichocarpa are important fast-growing woody plants,its wood is widely used in lignocellulosic biofuel production,paper,pulp and raw cellulose products.Cotton is one of the most important economic crops and it is an important source of fiber and oil.Because of genome sequencing work of Populus trichocarpa,Gossypium raimondii,Eucalyptus grandis have been completed,it is possible to analyze their LBD gene families at the genomic level.Therefore,we studied the LBD gene family in the Eucalyptus grandis,Populus trichocarpa,Gossypium raimondii and identified the key LBD genes that regulate the secondary growth.Our new findings provides new mechanisms to promote wood formation or increase fiber production.By using bioinformatics methods,a total of 46 LBD genes were identified in Eucalyptus grandis genome and were unevenly distributed on the 11 chromosomes.These genes could be classified into 2 classes?Class? and Class??including 8 subclasses??a,?b,?c,?d,?e,?f,?a and ?b?.The expression patterns of LBD gene family members in various tissues were detected by qRT-PCR,and three EgLBDs displayed xylem-?EgLBD29?or phloem-?EgLBD22 and EgLBD37?preferential expression.Confocal microscopy indicated that EgLBD22,EgLBD29 and EgLBD37 were localized to the nucleus.Furthermore,we found that EgLBD22,EgLBD29 and EgLBD37 were responsive to the treatments of indol-3-acetic acid and gibberellic acid.Functions of the selected EgLBDs were studied by ectopicallyoverexpressing in a hybrid poplar?Populus alba × Populus glandulosa?.More importantly,we demonstrated EgLBDs exerted different influences on secondary growth.Namely,35S::EgLBD37 led to significantly increased secondary xylem,35S::EgLBD29 led to greatly increased phloem fiber production,and 35S::EgLBD22 showing no obvious effects.Expression levels of genes in the EgLBD22-oe,EgLBD29-oe,EgLBD37-oe transgenic 84 K and wildtype84 K were investigated by RNA-seq.We revealed that key genes related to gibberellin,ethylene and auxin signaling pathway as well as cell expansion were significantly up-or down-regulated in transgenic 84 K.Our new findings suggest that EgLBD29 and EgLBD37 genes in E.grandis play important roles in secondary growth.This provides new methods to improve wood formation and fiber production.A total of 57 LBD genes were identified in Populus trichocarpa genome,their protein sequence of molecular weight and isoelectric point were predicted,these genes were distributed on 18 chromosomes and Scaffold₆5,Scaffold₈6.The structure of this gene family were simple whose introns number less than 2.According to the phylogenetic relationship,PtLBD genes could be classified into 2 classes including 7 subclasses.Analysis of gene expression patterns revealed that the expression of the family members has a certain spatial and temporal specificity,and response to nitrogen stress treatment.This study laid the foundation for studying the function of LBD genes in Populus trichocarpa.A total of 66 LBD genes were identified in Gossypium raimondii genome and were unevenly distributed on the 13 chromosomes.These genes could be classified into 2 classes including 6 subclasses.The structures of this gene family were simple with exons number less than 3.Fifteen conserved motifs were discovered from the GrLBD family members,and the conservative of LOB?Lateral Organ Boundaries?domain was analyzed.Analysis of gene expression patterns revealed that the expression of GrLBD genes have a certain spatial and temporal specificity.This study laid a foundation for the functional characterization of LBD genes in Gossypium raimondii.