Global analysis of the genome, transcriptome and epigenome in the diplosporous grass Eragrostis curvula (Schrad.) Nees

VIVIANA ECHENIQUE

Brasilia, Brasil.

Congreso; XX International Congress on Plant Reproduction; 2008

The Eragrostis curvula complex have a basic chromosome number of x = 10, and include a cytotype series with different ploidy levels (from 2x to 8x) and reproductive modes. The most valuable cultivars as forage are tetraploid and apomictic. This mode of reproduction is strongly related to ploidy. The aim of this work was to identify genetic, epigenetic and transcriptional changes associated to the reproductive mode in leaves and panicles of an euploid series obtained after a tetraploid-dihaploidization procedure followed by chromosome re-doubling with colchicine. Considerable levels of genome polymorphisms were detected between lines, showing markers (31.45% of 1008 RAPD and AFLP) with a revertant behavior (90 % of the polymorphic bands) following the changes of ploidy. This suggests that genome alterations were specific and conferred genetic structures characteristic of a given ploidy level. Polymorphic revertant sequences involved mostly non-coding regions, although some of them displayed sequence homology to known genes. Two per cent of the changes were related to the reproductive mode (apo vs sex). Changes in cytosine methylation patterns were also observed, affecting mainly coding regions (27 % of the 364 markers showed epigenetic variation). A comparative expression analysis based on ESTs showed that from 8,884 unigenes (inflorescence-derived libraries), 112 (1.26%) had significant differential expression in individuals with different ploidy level and/or reproductive mode. Independent comparisons between plants with different reproductive mode (same ploidy) or different ploidy level (same reproductive mode) allowed the identification of genes modulated in response to diplosporous development or polyploidization, respectively. A group of 50 genes were differencially expressed between the 4x sex and the other plant lines (2x sex, 4x apo) that exhibited highly similar expression patterns. DD analysis (4242 markers from panicles and 7622 from leaves), showed that the 4x apo and 4x sex gene expression profiles were more related and different from the 2x sex one (1.5 % and 9.29% were differential by the reproductive mode and ploidy level, respectively), but confirmed the expression of this particular group of genes (0.64%). As a difference of what happens with the 4x sex plant, the activation/silencing of these genes fail in the 4x diplosporous plant. Diplospory could be the consequence of this failure.