title: Deep sequencing on genome-wide scale reveals the unique composition and expression patterns of microRNAs in developing pollen of Oryza sativa.
abstract: BACKGROUND
  Pollen development in flowering plants requires strict control of the gene expression program and genetic information stability by mechanisms possibly including the miRNA pathway. However, our understanding of the miRNA pathway in pollen development remains limited, and the dynamic profile of miRNAs in developing pollen is unknown.
  
  
  RESULTS
  Using next-generation sequencing technology, we pyrosequenced small RNA populations from rice uninucleate microspores to tricellular pollen and control sporophytic tissues at the genome-wide level. We identified 292 known miRNAs, including members of all 20 families conserved in plants, and 75 novel miRNAs. Of the 292 known miRNAs, 202 were expressed, with 103 enriched, in developing pollen. More than half of these novel miRNAs displayed pollen-or stage-specific expression. Furthermore, analyzing the 367 miRNAs and their predicted targets indicated that correlation in expression profiles of pollen-enriched known miRNAs and their targets significantly differs from that of sporophyte-enriched known miRNAs and their targets in some functional terms, while novel miRNAs appeared to negatively regulate their targets. Importantly, gene ontology abundance analysis demonstrated chromatin assembly and disassembly was important in the targets of bicellular pollen-expressed novel miRNAs. Principal component analysis revealed pollen of all three stages was discriminated from sporophytes, largely because of the novel and non-conserved known miRNAs.
  
  
  CONCLUSIONS
  Our study, for the first time, revealed the differences in composition and expression profiles of miRNAs between developing pollen and sporophytes, with novel and non-conserved known miRNAs the main contributors. Our results suggest the important roles of the miRNA pathway in pollen development.
authors.affiliation: Research Center for Molecular and Developmental Biology, Key Laboratory of Photosynthesis and Environmental Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, 20 Nanxincun, Xiangshan, Beijing, China.
authors.forename: Li Qin
authors.initials: LQ
authors.lastname: Wei
authors.forename: Long Feng
authors.initials: LF
authors.lastname: Yan
authors.forename: Tai
authors.initials: T
authors.lastname: Wang
mesh_terms: D001483:Base Sequence; D016000:Cluster Analysis; D019295:Computational Biology; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D018745:Genome, Plant; D059014:High-Throughput Nucleotide Sequencing; D035683:MicroRNAs / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D012275:Oryza / Q000235:genetics* / Q000378:metabolism; D011058:Pollen / Q000235:genetics* / Q000378:metabolism; D015203:Reproducibility of Results; D016415:Sequence Alignment; D017423:Sequence Analysis, RNA
chemical_list: D035683:MicroRNAs