Characterization of retrotransposon sequences expressed in inflorescences of apomictic and sexual Paspalum notatum plants

Abstract

Apomixis, an asexual mode of reproduction through seeds, holds much promise for agricultural advances. However, the molecular mechanisms underlying this trait are still poorly understood. We previously isolated several transcripts representing novel sequences differentially expressed in reproductive tissues of sexual and apomictic plants. Here, we report the characterization of two of these unknown RNA transcripts (experimental codes N17 and N22). Since original fragments showed no significant homologies to sequences at databases, preliminary genomic PCR experiments were carried out to discard possible contaminations. RACE extension on flanking regions provided longer sequences for the candidates and additional related transcripts, which revealed similarity to LTR retrotransposons carrying short transduplicated segments of protein-coding genes. Interestingly, some transduplicated segments corresponded to genes previously associated with apomictic development. Gene copy number estimations revealed a moderate representation of the elements in the genome, with significantly increased numbers in a sexual genotype with respect to an apomictic one. Genetic mapping of N17 showed that a copy of this particular element was located onto Paspalum notatum linkage group F3c, at a central non-recombinant region resembling a centromere. Expression analysis showed an increased activity of N17 and N22 sense strands in ovules of the sexual genotypes. A retrotransposon-specific differential display analysis aimed at detecting related sequences allowed the identification of a complex family, with the majority of its members represented in the sexual genotype. Our results suggest that these elements could be participating in regulatory pathways related to apomixis and sexuality.

Increased apomixis expression concurrent with genetic and epigenetic variation in a newly synthesized Eragrostis curvula polyploid

“…Moreover, plant C expressed more transcripts related to retrotransposons. Our results are in agreement with those reported by Ochogavía et al23, who detected high rates of Gypsy retrotransposon expression in tetraploid sexual genotypes of Paspalum notatum when compared with apomictic genotypes of the same ploidy. Further work should analyze the role of these transposable elements in the transition from sexuality to apomixis.…”

Apomictic and Sexual Germline Development Differ with Respect to Cell Cycle, Transcriptional, Hormonal and Epigenetic Regulation

“…[32], [33], Paspalum spp. [34]–[36], apomeiotic mutants of Medicago falcata [37], Panicum maximum [38], and Poa pratensis [39], [40]. In addition, recent findings indicate spatial and temporal shifts in the expression of genes important for reproductive development between sexual and apomictic plants [27]–[29], [41].…”

Epigenetic control of cell specification during female gametogenesis

“…In many species, sexual diploids become apomictic after autopolyploidy, suggesting that dosage effects associated with ploidy might modify the expressivity of the trait (Carman 1997). In the grasses, discrete genomic regions sufficient for the inheritance of apomixis were discovered to be largely asyntenic, highly heterochromatic, recombinationally suppressed, and rich in transposable elements (TEs) particularly long terminal repeat (LTR) retrotransposons (Conner et al 2008;Huo et al 2009;Ochogavía et al 2011).…”