Abstract
This work was aimed at identifying genes that show altered expression profiles in response to changes in ploidy and/or reproductive mode (from sexual to apomictic) in the African grass Eragrostis curvula. A differential display analysis was performed on leaf and flower transcriptomes from a series of genetically related euploid plants, including tetraploid apomictic, diploid sexual, and tetraploid sexual plants. More than 100 primer combinations were used to generate 11,864 total markers, yielding 1293 differential bands. Of these bands, 11.84% to 6.74% were related to ploidy and 0.71% to 2.17% to the reproductive mode, depending on the tissue. A small percentage of bands showed similar expressions between the tetraploid apomictic and the diploid sexual plants. Expression-based similarity dendrograms were constructed. Our data suggested that ploidy is more decisive than tissue type in defining the transcriptome structure. Out of 102 fragments sequenced, 50 showed strong homology to known genes. The differentially expressed genes were mapped in silico onto maize chromosomes. Several candidates mapped within the linkage group syntenic to the Tripsacum dactyloides diplospory-governing region. The evidence indicates that expression of genes located around the diplospory-associated region may be strongly influenced by ploidy and may be silenced in the apomictic genotype. These findings are discussed in the context of diplospory molecular control and its connection with ploidy.
Highlights
Apomixis is an asexual reproduction mode, which generates clonal seeds with embryos genetically identical to the mother plant [1]
This series of plants is useful to identify genetic alterations and transcriptome repatterning that occurs immediately after a modification at the ploidy level, as well as for detecting genes associated with the expression of apomixis. Previous analysis of this series showed that all tetraploid plants shared a similar genetic structure, which differed to that of the diploid plant [32]. These results suggested that the genome response to ploidy variation was specific and conferred a genetic structure characteristic of a given ploidy level [32]
In the inflorescence Differential display (DD) experiments, we used 116 primer combinations that yielded high-quality amplification products to generate a total of 4242 markers
Summary
Apomixis is an asexual reproduction mode, which generates clonal seeds with embryos genetically identical to the mother plant [1]. This trait has been described in more than 400 species belonging to 40 angiosperm families [2]. While rare diploid cytotypes are sexual, polyploid ones are diplosporous apomicts [12]. E. curvula was classified as having an Antennaria-type embryo sac [13], but later it was re-classified as it’s own type, the Eragrostis-type, because it contains only four non-reduced nuclei at maturity instead of eight, as occurs in the Antennaria-type [14]. Embryos are formed by parthenogenesis, and fertilization of the polar nuclei (pseudogamy) is strictly required for endosperm development
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