Apospory appears to accelerate onset of meiosis and sexual embryo sac formation in sorghum ovules

Abstract

BackgroundGenetically unreduced (2n) embryo sacs (ES) form in ovules of gametophytic apomicts, the 2n eggs of which develop into embryos parthenogenetically. In many apomicts, 2n ES form precociously during ovule development. Whether meiosis and sexual ES formation also occur precociously in facultative apomicts (capable of apomictic and sexual reproduction) has not been studied. We determined onset timing of meiosis and sexual ES formation for 569 Sorghum bicolor genotypes, many of which produced 2n ES facultatively.ResultsGenotype differences for onset timing of meiosis and sexual ES formation, relative to ovule development, were highly significant. A major source of variation in timing of sexual germline development was presence or absence of apomictic ES, which formed from nucellar cells (apospory) in some genotypes. Genotypes that produced these aposporous ES underwent meiosis and sexual ES formation precociously. Aposporous ES formation was most prevalent in subsp. verticilliflorum and in breeding lines of subsp. bicolor. It was uncommon in land races.ConclusionsThe present study adds meiosis and sexual ES formation to floral induction, apomictic ES formation, and parthenogenesis as processes observed to occur precociously in apomictic plants. The temporally diverse nature of these events suggests that an epigenetic memory of the plants' apomixis status exists throughout its life cycle, which triggers, during multiple life cycle phases, temporally distinct processes that accelerate reproduction.

Natural Variation in Epigenetic Pathways Affects the Specification of Female Gamete Precursors in Arabidopsis

“…While several ecotypes and their hybrids exhibited variable frequencies of ectopic configurations, female gametophyte development occurred normally in all backgrounds, with a single meiotically derived cell differentiating into a functional megaspore, suggesting that in most cases ectopic cells degenerate without additional development. A similar pattern was observed in Sorghum bicolor, where the sporadic presence of aposporous initials correlated with an acceleration of meiotic initiation but no extranumerary female gametophytes were found at subsequent developmental stages (Carman et al, 2011). Our results favor the possibility of a flexible control of gamete precursor cell specification prevailing in Arabidopsis at the onset of meiosis, but a robust canalization mechanism acting at the onset of the processes that trigger meiosis and megagametogenesis; the molecular mechanisms that ensure the establishment of such a canalized developmental process could be partially dependent on the epigenetic pathways that involve AGO9 and RDR6.…”

Optimization of the conditions for Casuarina cunninghamiana Miq. genetic transformation mediated by Agrobacterium tumefaciens

“…There were no significant differences between OD 600 0.2 and 0.5 in the frequency of Km-resistant calli with GUS activity ( Table 3). As previously mentioned for long cocultivation time, an increased OD 600 could cause tissue necrotic because of the overgrowth of A. tumefaciens (Ribas et al 2011;Wang et al 2011). If the OD 600 was too low then few A. tumefaciens would transfer their T-DNA into target cells ).…”

Apomixis is not prevalent in subnival to nival plants of the European Alps

“…Apomixis, in contrast, is often associated with an acceleration of developmental pathways via maturation of embryo sacs before anthesis and pollination (e.g. Carman, 1997; Grimanelli et al , 2001; Carman et al , 2011). Such precocious development, known from alpine species of Alchemilla (Fröhner, 1990) and from Hieracium alpinum (Skawińska, 1963), would allow for rapid seed formation in a short growing season.…”