title: Identification, expression, and comparative genomic analysis of the IPT and CKX gene families in Chinese cabbage (Brassica rapa ssp. pekinensis).
abstract: BACKGROUND
  Cytokinins (CKs) have significant roles in various aspects of plant growth and development, and they are also involved in plant stress adaptations. The fine-tuning of the controlled CK levels in individual tissues, cells, and organelles is properly maintained by isopentenyl transferases (IPTs) and cytokinin oxidase/dehydrogenases (CKXs). Chinese cabbage is one of the most economically important vegetable crops worldwide. The whole genome sequencing of Brassica rapa enables us to perform the genome-wide identification and functional analysis of the IPT and CKX gene families.
  
  
  RESULTS
  In this study, a total of 13 BrIPT genes and 12 BrCKX genes were identified. The gene structures, conserved domains and phylogenetic relationships were analyzed. The isoelectric point, subcellular localization and glycosylation sites of the proteins were predicted. Segmental duplicates were found in both BrIPT and BrCKX gene families. We also analyzed evolutionary patterns and divergence of the IPT and CKX genes in the Cruciferae family. The transcription levels of BrIPT and BrCKX genes were analyzed to obtain an initial picture of the functions of these genes. Abiotic stress elements related to adverse environmental stimuli were found in the promoter regions of BrIPT and BrCKX genes and they were confirmed to respond to drought and high salinity conditions. The effects of 6-BA and ABA on the expressions of BrIPT and BrCKX genes were also investigated.
  
  
  CONCLUSIONS
  The expansion of BrIPT and BrCKX genes after speciation from Arabidopsis thaliana is mainly attributed to segmental duplication events during the whole genome triplication (WGT) and substantial duplicated genes are lost during the long evolutionary history. Genes produced by segmental duplication events have changed their expression patterns or may adopted new functions and thus are obtained. BrIPT and BrCKX genes respond well to drought and high salinity stresses, and their transcripts are affected by exogenous hormones, such as 6-BA and ABA, suggesting their potential roles in abiotic stress conditions and regulatory mechanisms of plant hormone homeostasis. The appropriate modulation of endogenous CKs levels by IPT and CKX genes is a promising approach for developing economically important high-yielding and high-quality stress-tolerant crops in agriculture.
authors.affiliation: Laboratory of Cell & Molecular Biology, Institute of Vegetable Science, Zhejiang University, 866 Yuhangtang Road, Hangzhou 310058, P,R,China. xlyu@zju.edu.cn.
authors.forename: Zhenning
authors.initials: Z
authors.lastname: Liu
authors.forename: Yanxia
authors.initials: Y
authors.lastname: Lv
authors.forename: Mei
authors.initials: M
authors.lastname: Zhang
authors.forename: Yapei
authors.initials: Y
authors.lastname: Liu
authors.forename: Lijun
authors.initials: L
authors.lastname: Kong
authors.forename: Minghua
authors.initials: M
authors.lastname: Zou
authors.forename: Gang
authors.initials: G
authors.lastname: Lu
authors.forename: Jiashu
authors.initials: J
authors.lastname: Cao
authors.forename: Xiaolin
authors.initials: X
authors.lastname: Yu
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000235:genetics*; D017360:Arabidopsis / Q000235:genetics; D029741:Brassica rapa / Q000201:enzymology / Q000235:genetics*; D002874:Chromosome Mapping; D055028:Comparative Genomic Hybridization; D017124:Conserved Sequence; D005091:Exons; D020440:Gene Duplication; D018506:Gene Expression Regulation, Plant; D020131:Genes, Duplicate; D018745:Genome, Plant; D007438:Introns; D005810:Multigene Family; D010088:Oxidoreductases / Q000235:genetics*; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics*; D011401:Promoter Regions, Genetic; D013312:Stress, Physiological
chemical_list: D010940:Plant Proteins; D010088:Oxidoreductases; C019984:cytokinin oxidase; D019883:Alkyl and Aryl Transferases; C024274:adenylate isopentenyltransferase