Genome-wide Identification,Expression Analysis And Evolutionary Relationships Of The IQ67-domain Gene Family In Common Wheat(Triticum Aestivum L.)

Bread wheat(Triticum aestivum L.),one of the three major cereal crops,is also one of the earliest crops domesticated by humans.It is widely grown all over the world and enriched in starch,protein,fat,minerals,and other nutrients,which provided more than 20% of global calory consumption.Recent studies have shown that the plant-specific IQ67-domain(IQD)gene family plays an important role in plant growth,development,and stress response.Based on the most updated hexaploid wheat genome,we conducted the genome-wide identification of IQD gene family in wheat.The phylogenetic relationship,gene structure and conserved motifs,and cis-element were also comprehensively analyized.The expression pattern of IQD gene in wheat tissue stage and under environmental stress was further investigated based on the RNA-seq datasets,and the co-expression and protein interaction network between IQD gene and other wheat genes were also constructed.Subsequently,the evolutionary relationship and population structure of the IQD gene family in wheat and its ancestral species were explored as well.The main results of this study are as follows:1.Through HMMER,BLAST and online databases,a total of 125 wheat IQD genes(TaIQDs)were identified in the whole genome,and they were named as TaIQD-1A/1B/1D-1～TaIQD-7A/7B/7D-3 according to the homology relationship between wheat subgenomes and the location of the gene on the chromosome.The phylogenetic tree classified the TaIQDs into four subgroups,and IQDs belonging to the same subgroup had similar gene structure and conserved motifs composition.2.The codon usage pattern of wheat IQD encoding genes was unbanlaced,and a total of 23(18.4%)IQD genes had an ENC value lower than 35,which suggested strong codon bias.Neutrality plot,ENC-plot,and PR2-plot analysis revealed that natural selection and mutation led to the codon preference of IQD encoding genes,with mutation rank the driven force.3.The expression pattern of wheat IQD gene was futher analyzed.A total of 50 and 64 IQD genes were expressed in the post-anthesis and embryonic stages of wheat,respectively.Several genes were specifically expressed,for example,TaIQD-2D-2 was highly expressed at 17 days post-anthesis.In addition,45 TaIQDs were expressed under cold stress,and the expressions of certain genes were highly induced by environmental stresses.Nine IQD genes were validated by q RT-PCR analysis,among which the expression levels of TaIQD-1A-7,TaIQD-2A-2 and TaIQD-3A-9 were significantly altered under salt,cold,heat,and drought stress,they may be future excellent candidate gene for functional gene research in wheat.4.Finally,the evolutionary pattern of IQD gene was analyzed.The polyploidization of wheat genome contribte greatly to the expansion of the IQD gene family.The expanded genes experienced strong purifying selection pressure.We detected 2,10,14,and 15 pairs of homologous genes with Ka/Ks > 1 in the homologous gene pairs of Triticum urartu,Aegilops tauschii,Triticum dicoccoides,Triticum turgidum,and Triticum aestivum,respectively.A small number of IQD genes may have been experienced strong positive selection pressure during evolution.In contrast,most homologous genes with Ka/Ks less than 1,revealing that IQD genes were mainly subjected to purifying selection pressure during evolution.Through resequencing data,the majority of TaIQD-related genes were located in the upstream and downstream regions of the TaIQDs,followed by intron regions.Population structure analysis showed that Triticum urartu,Aegilops tauschii and Triticum aestivum were highly differentiated.A certain degree of gene flow within and between subgroup was observed across different subgenomes.This study analyzed the biological functions and evolutionary relationships of the IQD gene family in wheat and revealed the evolutionary mechanism of IQD genes during polyploidization.