Genomic profiling of rice sperm cell transcripts reveals conserved and distinct elements in the flowering plant male germ lineage

Abstract

Summary Genomic assay of sperm cell RNA provides insight into functional control, modes of regulation, and contributions of male gametes to double fertilization. Sperm cells of rice (Oryza sativa) were isolated from field‐grown, disease‐free plants and RNA was processed for use with the full‐genome Affymetrix microarray. Comparison with Gene Expression Omnibus (GEO) reference arrays confirmed expressionally distinct gene profiles. A total of 10 732 distinct gene sequences were detected in sperm cells, of which 1668 were not expressed in pollen or seedlings. Pathways enriched in male germ cells included ubiquitin‐mediated pathways, pathways involved in chromatin modeling including histones, histone modification and nonhistone epigenetic modification, and pathways related to RNAi and gene silencing. Genome‐wide expression patterns in angiosperm sperm cells indicate common and divergent themes in the male germline that appear to be largely self‐regulating through highly up‐regulated chromatin modification pathways. A core of highly conserved genes appear common to all sperm cells, but evidence is still emerging that another class of genes have diverged in expression between monocots and dicots since their divergence. Sperm cell transcripts present at fusion may be transmitted through plasmogamy during double fertilization to effect immediate post‐fertilization expression of early embryo and (or) endosperm development.

Zygotic Genome Activation Occurs Shortly after Fertilization in Maize

“…This finding might explain the strongly condensed, compact sperm cell chromatin (see also Figure 1A). Indeed, a similar observation was reported for rice sperm cells (Russell et al, 2012;Anderson et al, 2013). Notably, no chromatin gene is among the TOP80 genes in maize egg cells.…”

Gene and Protein Expression Profiles in Rice Gametes and Zygotes: A Cue for Understanding the Mechanisms of Gametic and Early Zygotic Development in Angiosperms

“…Among 19 genes enriched in sperm cells, 9 were annotated as hypothetical proteins or genes (Table 30.2 ), being consistent with a previous report indicating enrichment of genes encoding proteins with unknown function in sperm-specifi c genes (Russell et al 2012 ). Os03g0661900 encodes a trypsin-like serine protease, and, in animals, serine proteases in the trypsin family can be expressed in sperm and involved in fertilization, although their molecular mechanisms during the fertilization process remain unknown (Sawada et al 1984(Sawada et al , 1996Baba et al 1994 ;Adham et al 1997 ).…”

Isolation of gametes from <i>Brachypodium distachyon</i>

“…Alternatively, direct analyses using isolated gametes or zygotes are possible, because procedures for isolating viable gametes/zygotes have been established in a wide range of plant species, including monocotyledonous and dicotyledonous plants (reviewed in Kranz 1999 andin Okamoto 2011;Yang et al 2014). The use of gametes, zygotes or embryos isolated from flowers of maize, wheat, rice, Arabidopsis and tobacco has enabled researchers to successfully identify genes expressed specifically or preferentially in male gametes, female gametes, or early embryos (Abiko et al 2013b;Anderson et al 2013;Borges et al 2008;Márton et al 2005;Ning et al 2006;Ohnishi et al 2011;Russell et al 2012;Sprunck et al 2005;Steffen et al 2007;Wang et al 2010;Wuest et al 2010;Yang et al 2006), since it has been supposed that genes expressing specifically/preferentially in gametes or early embryos function in reproductive or developmental processes such as gamete differentiation, gamete fusion, and early zygotic development. In addition to transcriptome-based analyses, single-cell-type proteomic approaches have widely been employed to determine the functions of specific cells (Dai and Chen 2012), and, recently, proteins expressing in rice gametes were globally identified (Abiko et al 2013a).…”