Deciphering apomixis-specific regions using Paspalum

PESSINO, SILVINA; ORTIZ, JUAN PABLO AMELIO; QUARIN, CAMILO LUIS; LEBLANC, OLIVIER; ESPINOZA, FRANCISCO

Bahía Blanca

Workshop; V Ciclo de seminarios sobre avances en la caracterización genética y molecular de la apomixis, CERZOS-CONICET, Bahía Blanca, 14-16 Noviembre 2016.; 2016

CERZOS-CONICET

Apomixis in flowering plants covers a wide range of reproductive behaviours that lead to seeds harbouring maternal embryos. Apomictic species likely evolved from sexual ancestors through alterations in the regulation of the core developmental programs governing sexual reproduction. They usually form agamic complexes; i. e. sexuality and apomixis are found in different cytological compartments, with the sexual plants usually restricted to the lowest ploidy level, while apomicts are polyploid. The developmental alterations underlying apomixis are genetically determined, but the nature of both the loci and the mechanisms remains under debate. Genetic studies in several grasses (Pennisetum squamulatum, Tripsacum dactyloides, Brachiaria decumbens, Paspalum notatum) have revealed that apomixis is under the control of a limited number of loci, usually mapped in a chromosomal region affected by suppression of recombination and biased transmission (so called Apomixis-Specific Region or ASR). Further cytogenetic and sequence characterization in Pennisetum and Paspalum have shown that the ASR contains both intact and truncated genic sequences, interspaced by large retrotransposon-rich sequences. Interestingly, in contrast to the complexity found in polyploid Paspalum notatum individuals, evidences in other Paspalum species indicate contrasted situations for the ASR organization and behaviour, including: expression of apomixis at the diploid level; lower or no suppression of recombination, and absence of transmission bias. These variations question the functional role of ASR structural organization in the transition from sexuality to apomixis. To understand both the ASR organization and its role in installing apomixis in plants, we recently initiated genome sequencing of a diploid Paspalum notatum genotype that shows some levels of apomixis expression. By using the most recent sequencing technologies in genotypes covering ASR variations, we will further produce genomic and epigenomic data, to identify both regulatory and genic sequences responsible for the ASR functional role. Moreover, we will explore the evolutionary forces that shaped its (epi)genomic patterns. With regard to this, evolutionary scenarios will also be discussed.