Functional Analyses Of BZIP Transcription Factor Family Genes Related To Anther Development And Stress Tolerance In Wheat

As one of the largest and most multifunctional transcription factor families in plants,bZIP(basic leucine zipper)family are involved in regulating various biological processes,including floral induction and development,stress response,hormone signaling,pathogen defense,photomorphogenesis,and seed maturation and germination.Wheat(Triticum aestivum L.)has been one of the most consumed and most widely cultivated food crops in the world,however,members of b ZIP transcription factor family in wheat had not been comprehensively identified and there had been not relevant reports about bZIP genes associated with anther development of wheat before this study.Meanwhile,extensive studies have shown that members of Subgroup A in the bZIP family play an important role in regulating the response to abiotic stress in plants,however,there are only a few reports about wheat Subgroup-A bZIP genes associated with stress tolerance.Additionally,wheat,T.urartu,Ae.tauschii,barley and Brachypodium are close relatives in the grass family,however,their real evolutionary relationship is still unknown to us.Results are as follows:1.187,98,96 and 107 members of bZIP transcription factor family were identified from wheat,T.urartu,Ae.tauschii and barley genomes,respectively.Orthology analysis of the bZIP family showed that 69.4% of b ZIP proteins in T.urartu were orthologous to 68.8% of bZIP proteins in Ae.tauschii.Wheat had more in-paralogs in the bZIP family than T.urartu,Ae.tauschii,barley and Brachypodium.The wheat b ZIP family were evolutionarily closer to the bZIP family of barley and Brachypodium than those of T.urartu and Ae.tauschii.2.Forty-eight differentially expressed TabZIP genes were identified from the comparison of Affymetrix microarray data of anthers between wheat male-sterile and restorer lines,and they were considered to be associated with anther development.TabZIP genes with close evolutionary relationship tended to have similar gene structure.Among the 23 selected TabZIP genes,15 TabZIP genes contained LTR cis-acting elements in their promoter regions.And the expression of 21 among these 23 TabZIP genes were obviously responsive to low temperature treatment.These 23 TabZIP genes all exhibited distinct tissue-specific expression pattern.Among them,11 TabZIP genes were expressed predominantly in anthers and most of them displayed over-dominance expression mode in the two-line hybrid combination TY806×BS366.Microarray data and expression analyses showed that TabZIP genes were probably involved in anther development.The study laid a foundation for selection and functional identification of genes associated with anther development.3.A total of 41 members of Subgoup A were identified from the wheat bZIP family.Phylogenetic analysis showed that most of Subgroup-A bZIP proteins associated with stress tolerance in Arabidopsis,rice and wheat were clustered in the A1 clade in the phylogenetic tree.And motif analysis showed that these bZIP proteins had similar conserved motifs.This study provide a comprehensive analysis of Subgroup-A members in the wheat b ZIP family,and put emphasis on members in Clade A1 that probably play an important role in regulating the response to abiotic stress.Gene structure analysis displayed that positions of introns within the hinge regions in bZIP domains were highly conserved while those within leucine zipper regions were diverse.Additionally,two groups of tandem paralogs and 11 groups of homologs were also identified from Subgroup A in the wheat b ZIP family.Subcellular localization showed that Tab ZIP27,TabZIP74,Tab ZIP138 and TabZIP174 proteins were localized in nucleus,while TabZIP9 protein was simultaneously localized in cell membrane,cytoplasm and nucleus.Gene expression analysis demonstrated that the expression of most of TabZIP genes of Subgroup A was responsive to ABA or various abiotic stress treatments.4.Overexpression of TabZIP174 raised the germination rate and improved the primary root growth of transgenic Arabidopsis under PEG treatment,and significantly improved their drought tolerance.Compared with wild-type Arabidopsis,transgenic Arabidopsis overexpressing TabZIP174 rapidly accumulated more free proline and soluble sugars,maintained a relatively steady osmatic potential,and had relatively lower water loss rates,higher survival rates and slower degradation rates of leaf chlorophyll under drought conditions.Besides,TabZIP174-overexpression increased the expression of RD29 A,RE29B,RAB18,DREB2 A,COR15A and COR47.The enhanced drought tolerance of transgenic Arabidopsis was probably attributed to the increased osmotic adjustment capacity.Phenotypic performance and physiological evidence suggest that TabZIP174 holds the potential in enhancing the stress tolerance and increasing the grain yield of crops.In summary,this study identified 187,98,96 and 107 members of bZIP family from the wheat,T.urartu,Ae.tauschii and barley genomes,respectively.69.4% of bZIP proteins in T.urartu were orthologous to 68.8% of bZIP proteins in Ae.tauschii.The wheat bZIP family were evolutionarily closer to the bZIP family of barley and Brachypodium than those of T.urartu and Ae.tauschii.Forty-eight differentially expressed TabZIP genes were identified by microarray data analysis of anthers.Among them,11 TabZIP genes were expressed predominantly in anthers and these TabZIP genes were probably involved in anther development.Besides,this study performed a series of bioinformatic analyses of Subgroup-A members in the wheat bZIP family,confirmed their subcellular localization and analyzed their gene expression profiles under stress conditions.And this study identified a wheat drought-resistance-related gene TabZIP174,and proposed the possible mechanism that TabZIP174 improved the drought tolerance of transgenic Arabidopsis.