Transcriptome And MiRNA Analyses Of Young Inflorescences In Wheat(triticum Aestivum L.)

Early inflorescence development in cereals is crucial for final grain number per spike,and hence the yield potential of the crop.To date,most of our understanding of the molecular regulatory pathways for inflorescence development is derived from model plants such as Arabidopsis thaliana and rice(Oryza sativa).However,no systematic analyses of gene expression profiles during this important process have been reported for common wheat(Triticum aestivum).To understand the molecular pathways regulating wheat inflorescence development,transcriptome analysis on shoot apical tissues at the spikelet initiation stage,the floret meristem initiation stage,the anther primordia initiation stage,and the young spike with immature florets were performed using mRNA-seq and small RNA-seq.ARGONAUTE proteins play key roles in miRNA-mediated gene silencing.The transcriptome analysis revealed that ARGONAUTE 1d(AGO1d)was specifically expressed at the anther primordia initiation stage.Together,the function of the ARGONAUTE 1d(AGO1d)gene was identified.1.In total,19,060 differentially expressed genes were identified and 24 k-means clusters displayed various gene expression patterns.464,357,428,and 5799 genes were considered to be specifically expressed at the spikelet initiation stage,the floret meristem initiation stage,the anther primordia initiation stage,and the young spike stage,respectively.Among these genes were homologs of important transcription regulators that may be involved in spikelet initiation,floret meristem specification,and floral organ patterning,as inferred from their homologs in model plants.Many orthologous transcription regulators for floral organ development are functionally conserved between rice and wheat,while expression pattern of genes involved in spikelet developmet or branch changed.2.Arabidopsis miRNAs involved in floral organ development,such as miR159,miR319,miR396,and miR167,were highly expressed in wheat inflorescences or young spike.The targets of these highly abundant miRNAs were accordingly regulated during wheat inflorescence development.RNA ligase-mediated rapid amplification of 5'-cDNA ends assays showed that these miRNAs were indeed all capable of cleaving the predicted targets.These results suggested that miRNA-mediated regulatory mechanisms for floral development may be conserved in cereals and Arabidopsis.3.AGO1 d was initially expressed in stamen primordia and later in the tapetum during anther maturation.The loss of function of the predominantly expressed B homoeolog of AGO1 d in a tetraploid durum wheat mutant resulted in smaller anthers with more infertile pollens than the wild type,and a reduced seed setting rate per spike,suggesting a role of this gene in anther development.Furthermore,our results validated our approach in identifying stage-specific genes during wheat inflorescence development that may have an effect on wheat grain yield.Together,this study provides a first glimpse of the gene regulatory networks in wheat young inflorescence development,highlighting potential targets for genetic manipulation to improve future wheat yields.