Environmental and Genetic Factors Affecting Apospory Expressivity in Diploid Paspalum rufum

Abstract

In angiosperms, gametophytic apomixis (clonal reproduction through seeds) is strongly associated with polyploidy and hybridization. The trait is facultative and its expressivity is highly variable between genotypes. Here, we used an F1 progeny derived from diploid apomictic (aposporic) genotypes of Paspalum rufum and two F2 families, derived from F1 hybrids with different apospory expressivity (%AES), to analyze the influence of the environment and the transgenerational transmission of the trait. In addition, AFLP markers were developed in the F1 population to identify genomic regions associated with the %AES. Cytoembryological analyses showed that the %AES was significantly influenced by different environments, but remained stable across the years. F1 and F2 progenies showed a wide range of %AES variation, but most hybrids were not significantly different from the parental genotypes. Maternal and paternal genetic linkage maps were built covering the ten expected linkage groups (LG). A single-marker analysis detected at least one region of 5.7 cM on LG3 that was significantly associated with apospory expressivity. Our results underline the importance of environmental influence in modulating apospory expressivity and identified a genomic region associated with apospory expressivity at the diploid level.

Variation of Residual Sexuality Rates along Reproductive Development in Apomictic Tetraploids of Paspalum

“…Previous studies identified relevant factors influencing this competition in favor of the sexual or apomictic pathways. These factors can be gathered in numerous groups: polyploidy [2,9,23,27,48]; hybridization [2,48]; sexual pathway deregulation [14,49]; differential gene expression in the ovule [2,8,14,30,31,50]; inbreeding depression [31]; genetic disharmony in seminal tissues [51][52][53] (i.e., EBN, imprinting); light regime [11,23]; water stress [9,25]; environmental conditions [10,41]; seasonal variation of the flowering time [23,24]; pollination timing [28,54]; precocious development and parthenogenesis [21,30,31,48,55,56]. Studies suggest that a combination of all or some of these factors may be at play, affecting the reproductive pathways in the ovule [57].…”

“…are agamic complexes composed of sexual diploids (2n = 2x = 20) and facultative apomictic tetraploids (2n = 4x = 40) [38][39][40]. Previous studies in Paspalum species established that genetic or epigenetic background, ploidy levels, as well as environmental factors, influence the observed rates of apomixis and sexuality [23,24,31,41]. On one hand, diploids of Paspalum are able to produce aposporous embryo sacs, but seeds are only sexually produced [27,39,[42][43][44], although low rates of functional apomixis were recently noticed [45,46].…”

Environmental influence on reproductive traits of buffel grass facultative apomictic genotypes and its implication in plant breeding

“…As can be noticed, and as postulated by Kumar (2017), the epigenetic control of apomixis is an emerging theory, with growing evidence (Karunarathne et al, 2020;Mateo de Arias, 2015;Podio et al, 2014;Rios et al, 2013;Soliman et al, 2021) in several species. Epigenetic changes and alterations in gene expression, particularly through DNA methylation, provide a means to achieve desirable phenotypic plasticity and adaptive advantages (Kumar et al, 2019).…”

“…The epigenetic control of apomixis expression is an emerging theory that suggests that apomixis is reversibly superimposed upon sexuality (Kumar, 2017). Although there is evidence of epigenetic control of the reproductive mode in several Poaceae species (Karunarathne et al, 2020;Reutemann et al, 2022;Rios et al, 2013;Soliman et al, 2021), the environmental influence on apospory/sexual expression throughout the flowering season has been scarcely explored in buffel grass (Gounaris et al, 1991;Hussey et al, 1991) under field conditions. Buffel grass is a protogynous (Shafer et al, 2000) and mainly cross-pollinated (Hanselka et al, 2004) species with variable levels of self-compatibility.…”

Apomixis: oh, what a tangled web we have!

“…Transcriptome-wide changes at the onset of apomixis have been documented in several apomictic species (Hand and Koltunow 2014 ) and a global decrease in gene expression at the early stages of development in apomictic versus sexual individuals has been recorded in Boechera divaricarpa (Sharbel et al 2010 ), Hypericum perforatum (Galla et al 2017 ), Eragrostis curvula (Rodrigo et al 2017 ; Garbus et al 2019 ) and Paspalum Rufum (Soliman et al 2021 a, b). Transcriptional profiling of Arabidopsis embryos demonstrated that heterochrony of specific transcripts is more significant than spatial regulation (Spencer et al 2007 ), suggesting that timing of gene expression is critical in early development.…”