Apospory expressivity modulation by environmental and epigenetic changes in diploid genotypes of Paspalum rufum

MARIANO, SOLIMAN; PODIO, MARICEL; MARCONI, GIANPIERO; DI MARSICO, MARCO; JUAN PABLO A. ORTIZ; ALBERTINI, EMIDIO; DELGADO LUCIANA

Conferencia; International Conference on sexual plant reproduction; 2022

In angiosperms, gametophytic apomixis is strongly associated with polyploidy and hybridization. Most apomictic polyploids are facultative, and apomixis and sexuality coexist in the same plant or even in the same ovary, but finally, only apomixis succeeds. At the diploid level, the opposite occurs, and although some genotypes can produce aposporous embryo sacs (AES), the seeds derived from sexuality. We previously observed that some natural diploid genotypes of Paspalum rufum could reproduce by apomixis, and also aposopory expressivity could be significantly increased by hybridisation. In this context, here we explore environmental stability and epigenetic variation associated with the trait at the diploid level on P. rufum. Apospory expressivity (%AES) was evaluated by cytoembryological analyses of diploid sibling genotypes of P. rufum exposed to two different environments and across the years. DNA methylation levels (at CG, CHG, and CHH contexts) were analysed using a methylation content sensitive enzyme ddRAD (MCSeEd) strategy. Full spikelets (at pre meiosis/meiosis and post-meiosis stages) of full sibling diploid P. rufum genotypes with differential %AES were compared. Our analysis showed that the %AES was significantly influenced by different environments but remained stable across the years. Principal component analysis and heatmaps, based on the relative methylation level, discriminated samples with contrasting apospory expressivity. Differential methylated contigs (DMCs) showed 14% of homology to known transcripts of Paspalum notatum reproductive transcriptome, and almost all of them were also differentially expressed between apomictic and sexual samples. DMCs showed homologies to genes involved in flower growth, development, and apomixis. Moreover, a high proportion of the DMCs aligned on genomic regions associated with apomixis in Setaria italica. Our results underline the importance of environmental influence in modulating apospory expressivity and identified several stage-specific differential methylated sequences associated with apospory expressivity, which could guide future functional gene characterisation concerning apomixis success at diploid and tetraploid levels.