title: Comprehensive analysis of tobacco pollen transcriptome unveils common pathways in polar cell expansion and underlying heterochronic shift during spermatogenesis.
abstract: BACKGROUND
  Many flowering plants produce bicellular pollen. The two cells of the pollen grain are destined for separate fates in the male gametophyte, which provides a unique opportunity to study genetic interactions that govern guided single-cell polar expansion of the growing pollen tube and the coordinated control of germ cell division and sperm cell fate specification. We applied the Agilent 44 K tobacco gene chip to conduct the first transcriptomic analysis of the tobacco male gametophyte. In addition, we performed a comparative study of the Arabidopsis root-hair trichoblast transcriptome to evaluate genetic factors and common pathways involved in polarized cell-tip expansion.
  
  
  RESULTS
  Progression of pollen grains from freshly dehisced anthers to pollen tubes 4 h after germination is accompanied with > 5,161 (14.9%) gametophyte-specific expressed probes active in at least one of the developmental stages. In contrast, > 18,821 (54.4%) probes were preferentially expressed in the sporophyte. Our comparative approach identified a subset of 104 pollen tube-expressed genes that overlap with root-hair trichoblasts. Reverse genetic analysis of selected candidates demonstrated that Cu/Zn superoxide dismutase 1 (CSD1), a WD-40 containing protein (BP130384), and Replication factor C1 (NtRFC1) are among the central regulators of pollen-tube tip growth. Extension of our analysis beyond the second haploid mitosis enabled identification of an opposing-dynamic accumulation of core regulators of cell proliferation and cell fate determinants in accordance with the progression of the germ cell cycle.
  
  
  CONCLUSIONS
  The current study provides a foundation to isolate conserved regulators of cell tip expansion and those that are unique for pollen tube growth to the female gametophyte. A transcriptomic data set is presented as a benchmark for future functional studies using developing pollen as a model. Our results demonstrated previously unknown functions of certain genes in pollen-tube tip growth. In addition, we highlighted the molecular dynamics of core cell-cycle regulators in the male gametophyte and postulated the first genetic model to account for the differential timing of spermatogenesis among angiosperms and its coordination with female gametogenesis.
authors.affiliation: Laboratory of Pollen Biology, Institute of Experimental Botany, Academy of Sciences of the Czech Republic, Rozvojová 263, 165 02 Praha 6, Czech Republic.
authors.forename: Said
authors.initials: S
authors.lastname: Hafidh
authors.forename: Katarína
authors.initials: K
authors.lastname: Breznenová
authors.forename: Petr
authors.initials: P
authors.lastname: Růžička
authors.forename: Jana
authors.initials: J
authors.lastname: Feciková
authors.forename: Věra
authors.initials: V
authors.lastname: Capková
authors.forename: David
authors.initials: D
authors.lastname: Honys
mesh_terms: D017360:Arabidopsis / Q000235:genetics; D002453:Cell Cycle / Q000235:genetics; D056130:Gametogenesis, Plant; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D055785:Gene Knockdown Techniques; D018525:Germination; D020411:Oligonucleotide Array Sequence Analysis; D018517:Plant Roots / Q000235:genetics; D011058:Pollen / Q000235:genetics*; D053205:Pollen Tube / Q000254:growth & development; D018749:RNA, Plant / Q000235:genetics; D014026:Nicotiana / Q000235:genetics*; D059467:Transcriptome
chemical_list: D018749:RNA, Plant