Genome-wide Identification And Transcriptome Analysis Of Aquaporin Gene Family In Nicotiana Tabacum

Tobacco is one of major economic crop,whose planting usually encounters drought,cold,and low-potassium stresses.As major intrinsic protein,aquaporin(AQP)regulates the development process about the flowering,stomatal movement,cell elongation and differentiation,and adversity stresses.Mining the potential AQP resistance genes is conducive to the genetic improvement of planting,further improving the quality and yield of tobacco.In this study,we identified the AQP gene family based on the K326 genome,and analyzed a series of bioinformatic tests,including nomenclature and grouping,the prediction of physicochemical property,the study of evolutionary relationship and transcriptome analysis,which will contribute to genetic exploration and functional analysis of AQPs.The results are as follows:1.A total of 101 NtAQPs were identified.AQPs from Arabidopsis,rice,poplar and tobacco were constructed phylogenetic tree.According to the homology relationship,NtAQPs were divided into five subfamilies: PIPs,TIPs,NIPs,SIPs and XIPs.Each subfamily subdivided into different subgroups: 2 PIPs,5 TIPs,7 NIPs,2 SIPs and 2 XIPs.2.Multiple sequence alignments showed that the amino acid structures of NtAQPs in each subfamily were relatively conserved,and most NtAQPs contained 2 NPA motifs,relatively conserved Ar/R(Aromatic/Arginine)selectivity filter,and Froger' sites.Most NtAQPs were localized on the plasma membrane and vacuole membrane,while NtPIP1-13 and NtPIP1-15 were present on the endoplasmic reticulum.Although the number of transmembrane structural regions of NtAQPs ranged from 2 to 8,six transmembrane regions predominated in NtAQPs.NtAQPs were mainly composed of alpha helix,random coil and extended chain,and several NtNIPs also have a small amount of beta turn.3.It is similar for the motif distribution and gene structure of NtAQPs in the same subfamily,but some NtAQPs were inconsistent within same subfamily.Genome location showed that most of them were unevenly distributed on chromosomes and gene pairs(NtPIP2-3/NtPIP2-6 on Chr02 and NtTIP1-6/NtTIP1-8,NtNIP1-3/NtNIP2-1,NtPIP2-13/NtPIP2-15 on scaffold)had occurred tandem duplication events.4.10 NtAQP pairs had a collinearity relationship,which suggested that most of NtAQP pairs might have similar functions during evolution due to structural similarity.Specially,three NtXIPs(NtXIP2-2,NtXIP3-3,NtXIP3-4)with multiple collinearity relationship easily appeared functional differentiation due to different gene structures and expression patterns.Promoter regions of NtAQPs mainly contained cis-acting elements about hormone response,abiotic stress,and clock regulation,among which,the cis-acting elements containing plant hormone responsive,anaerobic induction,and light responsive were most widespread in NtAQPs.5.NtAQPs had various expression patterns in tobacco root,stem,and shoot apex at different time.The tandem duplicated NtPIP2-3/NtPIP2-6 and collinear NtTIP4-1/NtTIP4-2 had similar expression patterns in three tissues,which suggested that these genes might have same transport activity.While NtAQPs with collinear relationship such as NtTIP2-9/NtTIP2-10,NtTIP2-11/NtTIP2-12 were prone to functional differentiation in shoot apex.NtPIP1-10,NtPIP2-3,NtPIP2-5,NtPIP2-6 were considered as potential resistance genes due to significantly up-regulated after low-potassium treatment in tobacco.