Authors: Riccardo Aiese CiglianoGaetana CremonaRosa PaparoPasquale TermolinoGiorgio PerrellaRuben GutzatMaria Federica ConsiglioClara Conicella

Institutions:

  • National Research Council of Italy, Institute of Plant Genetics, Research Division Portici, 80055 Portici, Italy (R.A.C., G.C., R.P., P.T., G.P., M.F.C., C.C.);
  • Sequentia Biotech, Barcelona, Spain

Publication: Plant Physiology

Date: September 2013

Full paper: http://www.plantphysiol.org/content/163/1/431

Abstract:

Histone modifications are involved in the regulation of many processes in eukaryotic development. In this work, we provide evidence that AtHDA7, a HISTONE DEACETYLASE (HDAC) of the Reduced Potassium Dependency3 (RPD3) superfamily, is crucial for female gametophyte development and embryogenesis in Arabidopsis (Arabidopsis thaliana). Silencing of AtHDA7 causes degeneration of micropylar nuclei at the stage of four-nucleate embryo sac and delay in the progression of embryo development, thereby bringing the seed set down in the Athda7-2 mutant. Furthermore, AtHDA7 down- and up-regulation lead to a delay of growth in postgermination and later developmental stages. The Athda7-2 mutation that induces histone hyperacetylation significantly increases the transcription of other HDACs (AtHDA6 and AtHDA9). Moreover, silencing of AtHDA7 affects the expression of ARABIDOPSIS HOMOLOG OF SEPARASE (AtAESP), previously demonstrated to be involved in female gametophyte and embryo development. However, chromatin immunoprecipitation analysis with acetylated H3 antibody provided evidence that the acetylation levels of H3 at AtAESP and HDACs does not change in the mutant. Further investigations are essential to ascertain the mechanism by which AtHDA7 affects female gametophyte and embryo development.

DNA of eukaryotic cells is associated with nuclear proteins to form the chromatin. Its basic unit is the nucleosome, which is composed of about 147 bp of DNA bound to an octamer of the canonical histones H3, H4, H2A, and H2B (Berr et al., 2011). Histone posttranslational modifications contribute to define chromatin states that drive different chromatin-based nuclear processes. In fact, histone posttranslational modifications, including acetylation, methylation, phosphorylation, and ubiquitination, control fundamental processes such as transcription (Bell et al., 2011), DNA replication (Ehrenhofer-Murray, 2004), cell cycle (O’Sullivan et al., 2010), DNA repair (Soria et al., 2012), and recombination (Perrella et al., 2010). Histone acetylation is carried out by histone acetylases (HATs), while it is erased by histone deacetylases (HDACs). Plant HDACs are grouped into three families: the RDP3/HDA1 superfamily, SIR2, and HD2 (Pandey et al., 2002). Two of these families are homologous to the classes of HDACs found in yeast and animals, while the HD2 class appears to be unique to plants and unrelated to the other classes. In Arabidopsis (Arabidopsis thaliana), 18 putative HDACs have been identified (Pandey et al., 2002). Some HDACs are emerging as crucial players in plant growth and development processes, including embryogenesis, flowering, meiosis, senescence, as well as responses to environmental cues (Hollender and Liu, 2008Berr et al., 2011). In particular, mutations in genes encoding HDACs as well as treatments with trichostatin A (TSA), an inhibitor of HDACs, highlighted a requirement of the HDACs in reproductive development. Indeed, the down-regulation of AtHDA19 induced delayed flowering, flower abnormalities, embryonic defects, and seed set reduction (Tian et al., 2003). Silencing as well as overexpression of AtHD2A severely affected seed development (Wu et al., 2000Zhou et al., 2004). The Athda6 mutant was reported to exhibit reduced fertility to some extent (Aufsatz et al., 2002), and mutation of AtHDA9 led to an early-flowering phenotype in short-day-grown plants (Kim et al., 2013). Some findings strongly suggest a role for AtHDA7 in Arabidopsis reproduction. Indeed, AtHDA7 (At5g35600), encoding a putative HDAC of the Reduced Potassium Dependency3 (RPD3) superfamily, is preferentially expressed in flower bud (Schmid et al., 2005) and is up-regulated in microdissected hyperacetylated microsporocytes (Barra et al., 2012). To investigate the unexplored function of AtHDA7, we analyzed overexpression and silenced mutants, thereby proving that AtHDA7 is required for female gametophyte development and embryogenesis progression. Moreover, AtHDA7 down- and up-regulation lead to a delay of growth in postgermination and later developmental stages.