Search Results (3)

Seed initiation in Arabidopsis depends on regulatory transitions that begin before fertilization, yet these events are often treated as separate developmental episodes rather than as a connected sequence. Here, we synthesize evidence from megaspore mother cell (MMC) specification to endosperm cellularization and ask whether particular stage boundaries meet a narrow definition of developmental handover: a shift between dominant control logics, with detectable first-order consequences in the ensuing interval and acknowledged overlap across the boundary. This framework goes beyond canonical staging by distinguishing chronological succession from shifts in regulatory control, thereby clarifying where earlier states are expected to constrain later outcomes, which developmental boundaries are mechanistically well supported, and where further mechanistic resolution is most needed. We first examine how MMC singleness (restriction to a single reproductive founder cell per ovule primordium) emerges through coupled sporophytic restriction and local competence. We then consider how meiosis and female gametophyte maturation establish regulatory poise (an actively restrained and asymmetric mature female-gametophytic state), including cell-cycle restraint, companion-cell-restricted demethylation, and unequal gametic chromatin states that condition subsequent embryo and endosperm behavior. After fertilization, release of central-cell restraint, activation of an endosperm auxin program, and recruitment of maternal tissues together mark the onset of seed initiation. In this view, syncytial endosperm is an actively maintained developmental state shaped by parental dosage, epigenetic control, hormone signaling, and maternal interaction, whereas endosperm cellularization represents a regulated switch with seed-wide consequences. In Arabidopsis, the clearest handover is the mature female gametophyte-to-fertilization boundary, whereas the boundaries linking MMC specification to female gametophyte maturation and syncytial endosperm to cellularization remain provisional. Full article

Strigolactones (SLs) were recently defined as a novel class of plant hormones that act as key regulators of diverse developmental processes and environmental responses. Much research has focused on SL biosynthesis and signaling in roots and shoots, but little is known about whether SLs are produced in early developing seeds and about their roles in ovule development after fertilization. This study revealed that the fertilized ovules and early developing pericarp in Xanthoceras sorbifolium produced minute amounts of two strigolactones: 5-deoxystrigol and strigol. Their content decreased in the plants with the addition of exogenous phosphate (Pi) compared to those without the Pi treatment. The exogenous application of an SL analog (GR24) and a specific inhibitor of SL biosynthesis (TIS108) affected early seed development and fruit set. In the Xanthoceras genome, we identified 69 potential homologs of genes involved in SL biological synthesis and signaling. Using RNA-seq to characterize the expression of these genes in the fertilized ovules, 37 genes were found to express differently in the fertilized ovules that were aborting compared to the normally developing ovules. A transcriptome analysis also revealed that in normally developing ovules after fertilization, 12 potential invertase genes were actively expressed. Hexoses (glucose and fructose) accumulated at high concentrations in normally developing ovules during syncytial endosperm development. In contrast, a low ratio of hexose and sucrose levels was detected in aborting ovules with a high strigolactone content. XsD14 virus-induced gene silencing (VIGS) increased the hexose content in fertilized ovules and induced the proliferation of endosperm free nuclei, thereby promoting early seed development and fruit set. We propose that the crosstalk between sugar and strigolactone signals may be an important part of a system that accurately regulates the abortion of ovules after fertilization. This study is useful for understanding the mechanisms underlying ovule abortion, which will serve as a guide for genetic or chemical approaches to promote seed yield in Xanthoceras. Full article

Endosperm development in barley starts with the formation of a multinucleate syncytium, followed by cellularization in the ventral part of the syncytium generating endosperm transfer cells (ETCs) as first differentiating subdomain, whereas aleurone (AL) cells will originate from the periphery of the enclosing syncytium. Positional signaling in the syncytial stage determines cell identity in the cereal endosperm. Here, we performed a morphological analysis and employed laser capture microdissection (LCM)-based RNA-seq of the ETC region and the peripheral syncytium at the onset of cellularization to dissect developmental and regulatory programs directing cell specification in the early endosperm. Transcriptome data revealed domain-specific characteristics and identified two-component signaling (TCS) and hormone activities (auxin, ABA, ethylene) with associated transcription factors (TFs) as the main regulatory links for ETC specification. On the contrary, differential hormone signaling (canonical auxin, gibberellins, cytokinin) and interacting TFs control the duration of the syncytial phase and timing of cellularization of AL initials. Domain-specific expression of candidate genes was validated by in situ hybridization and putative protein–protein interactions were confirmed by split-YFP assays. This is the first transcriptome analysis dissecting syncytial subdomains of cereal seeds and provides an essential framework for initial endosperm differentiation in barley, which is likely also valuable for comparative studies with other cereal crops. Full article