Eragrostis curvula, a Model Species for Diplosporous Apomixis

Abstract

Eragrostis curvula (Schrad.) Ness is a grass with a particular apomictic embryo sac development called Eragrostis type. Apomixis is a type of asexual reproduction that produces seeds without fertilization in which the resulting progeny is genetically identical to the mother plant and with the potential to fix the hybrid vigour from more than one generation, among other advantages. The absence of meiosis and the occurrence of only two rounds of mitosis instead of three during embryo sac development make this model unique and suitable to be transferred to economically important crops. Throughout this review, we highlight the advances in the knowledge of apomixis in E. curvula using different techniques such as cytoembryology, DNA methylation analyses, small-RNA-seq, RNA-seq, genome assembly, and genotyping by sequencing. The main bulk of evidence points out that apomixis is inherited as a single Mendelian factor, and it is regulated by genetic and epigenetic mechanisms controlled by a complex network. With all this information, we propose a model of the mechanisms involved in diplosporous apomixis in this grass. All the genetic and epigenetic resources generated in E. curvula to study the reproductive mode changed its status from an orphan to a well-characterised species.

Apomixis: oh, what a tangled web we have!

“…The authors suggested that this was due to novel epigenetic regulation associated with the transition to polyploidy (Zappacosta et al 2014 ). Variations in methylation patterns in Eragrostis curvula were also detected after autopolyploidization by Cervigni et al ( 2008 ), Ochogavía et al ( 2011 ) and (Carballo et al 2021 ). Similarly, methylation analyses revealed that new epialleles emerged after tetraploidization of a diploid Paspalum notatum (Rodriguez et al 2012 ) and P. rufum (Siena et al 2008 ).…”

“…Protein degradation pathway genes, codifying for F-box proteins, E3 ligases-like, the homolog of RMA3 and a TRAF-like superfamily protein, and ubiquitin-like superfamily protein like UBC28 , were found to be upregulated in apomictic nucella of Boechera (Zühl et al 2019 ). The ubiquitination pathway was differentially expressed in Eragrostis curvula (Carballo et al 2021 ) under drought stress, with five genes down- and two upregulated (Selva et al 2020 ). The Apospory locus ( HAPPY ) of Hypericum perforatum includes a homolog of ARIADNE7 , a protein involved in regulatory processes and protein degradation (Schallau et al 2010 ).…”

From tetraploid to diploid, a pangenomic approach to identify genes lost during synthetic diploidization of Eragrostis curvula

“…In this study, a pangenomic approach was adopted to unravel genome diversity in E. curvula species. Even though this grass is studied as an apomictic model ( Carballo et al., 2021b ), here, we focused on the alterations produced by a recent diploidization event ( Echenique et al., 1996 ) of the tetraploid cv. Tanganyika INTA to produce the Victoria genotype, obtained by in vitro culture of inflorescences ( Cardone et al., 2006 ).…”

“…All the genes assessed here are, at some point, associated with both reproduction and ploidy level. Regarding the genes that are absent in Victoria, it is important to note that after diploidization, the reproductive performance of Victoria was seriously affected ( Carballo et al., 2021b ). The lack of some genes such as RECQ4A , MEE66 , and PVA12 , which are directly involved in the reproductive pathway, could be the cause of the reduction in fertility.…”

Asexual reproduction through seeds: the complex case of diplosporous apomixis

“…2F). The mature gametophyte contains one egg cell, two synergid cells, and only one mononucleate central cell; hence, it is possible to maintain the 2:1 maternal:paternal genome contribution to the endosperm, to which cereals are very sensitive (Meier et al, 2011;Carballo et al, 2021) (Table 1).…”