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The phenology of organisms corresponds to the temporal match between the components of their life cycle and the seasonal distribution of resources and hazards. Flowering has been extensively studied to describe the reproductive phenology of plants, but in comparison, other key events for reproductive success such as the seed maturation period and the time of seed dispersal have been considerably less investigated.This study describes the temporal sequence of onset of flowering and seed dispersal, and the time necessary to mature seeds in 138 species growing in the strongly seasonal climate of Mediterranean southern France. Data for the three traits were compiled from several original surveys to characterize the reproductive phenology of 47 annual, 67 perennial herbaceous and 24 low stature woody species. The timing of these three phases was assessed in relation to local climatic conditions, and the degree to which they were coordinated was tested.All three phenological traits spanned a wide range of values from early spring to late summer. Annuals flowered slightly earlier than perennials but the largest difference between these groups was found for the seed maturation period, which was much shorter in annuals. This resulted in earlier dispersal dates in these species, which occurred before periods of high water deficit. Significant positive correlations were found between onset of flowering, onset of seed dispersal and seed maturation period. This suggests a consistent pattern of coordination between the different phases of reproductive phenology across species.Our results show that while the time slot for flowering appears restricted to periods with adequate temperature and water availability for most species, the seed maturation period and dispersal phase can occur during periods of substantial water deficit, at least for perennials. They also suggest that the different species can be arrayed along a fast-slow continuum based on reproductive events, from early flowering species with short seed maturation and early dispersal to late flowering species with long seed maturation and late dispersal. Whether this relates to the postulated fast-slow continuum identified for the functioning of vegetative organs is a promising avenue for future research.

Key message A seed maturation protein gene ( CaSMP ) from Coffea arabica is expressed in the endosperm of yellow/green fruits. The CaSMP promoter drives reporter expression in the seeds of immature tomato fruits. In this report, an expressed sequence tag-based approach was used to identify a seed-specific candidate gene for promoter isolation in Coffea arabica . The tissue-specific expression of the cognate gene ( CaSMP ), which encodes a yet uncharacterized coffee seed maturation protein, was validated by RT-qPCR. Additional expression analysis during coffee fruit development revealed higher levels of CaSMP transcript accumulation in the yellow/green phenological stage. Moreover, CaSMP was preferentially expressed in the endosperm and was down-regulated during water imbibition of the seeds. The presence of regulatory cis -elements known to be involved in seed- and endosperm-specific expression was observed in the CaSMP 5′-upstream region amplified by genome walking (GW). Additional histochemical analysis of transgenic tomato (cv. Micro-Tom) lines harboring the GW-amplified fragment (~ 1.4 kb) fused to uidA reporter gene confirmed promoter activity in the ovule of immature tomato fruits, while no activity was observed in the seeds of ripening fruits and in the other organs/tissues examined. These results indicate that the CaSMP promoter can be used to drive transgene expression in coffee beans and tomato seeds, thus representing a promising biotechnological tool.

The seed maturation programme occurs only during the late phase of embryo development, and repression of the maturation genes is pivotal for seedling development. However, mechanisms that repress the expression of this programme in vegetative tissues are not well understood. A genetic screen was performed for mutants that express maturation genes in leaves. Here, it is shown that mutations affecting SDG8 (SET DOMAIN GROUP 8), a putative histone methyltransferase, cause ectopic expression of a subset of maturation genes in leaves. Further, to investigate the relationship between SDG8 and the Polycomb Group (PcG) proteins, which are known to repress many developmentally important genes including seed maturation genes, double mutants were made and formation of somatic embryos was observed on mutant seedlings with mutations in both SDG8 and EMF2 (EMBRYONIC FLOWER 2). Analysis of histone methylation status at the chromatin sites of a number of maturation loci revealed a synergistic effect of emf2 and sdg8 on the deposition of the active histone mark which is the trimethylation of Lys4 on histone 3 (H3K4me3). This is consistent with high expression of these genes and formation of somatic embryos in the emf2 sdg8 double mutants. Interestingly, a double mutant of sdg8 and vrn2 (vernalization2), a paralogue of EMF2, grew and developed normally to maturity. These observations demonstrate a functional cooperative interplay between SDG8 and an EMF2-containing PcG complex in maintaining vegetative cell identity by repressing seed genes to promote seedling development. The work also indicates the functional specificities of PcG complexes in Arabidopsis.

Mature dry legume seeds may contain up to 30 different soluble carbohydrates. Sucrose is a major component of the total soluble carbohydrates; others include the raffinose family oligosaccharides (RFOs; raffinose, stachyose, verbascose) that are mono-, di- and tri-α-galactosyl derivatives of sucrose. Other galactosides may include α-galactosyl derivatives of the cyclitols myo-inositol (galactinol, digalactosyl myo-inositol and trigalactosyl myo-inositol), d-pinitol (galactopinitol A, digalactosyl pinitol A (ciceritol) and trigalactosyl pinitol A; and galactopinitol B; higher galactosyl oligomers of galactopintiol B have rarely been detected), d-chiro-inositol (fagopyritol B1, fagopyritol B2 and fagopyritol B3) and d-ononitol (galactosyl d-ononitol and digalactosyl d-ononitol). Small amounts of myo-inositol, d-pinitol and d-chiro-inositol may also be present. Raffinose, stachyose and verbascose increase late in seed maturation, with 70% of RFOs accumulating after maximum seed dry weight is attained. RFOs are mostly degraded during germination. Sucrose, myo-inositol, d-pinitol and d-chiro-inositol are synthesized in maternal tissues of some legumes and are transported to and unloaded by seed coats into the apoplastic space surrounding developing seed embryos. Free cyclitols may be 60% of total soluble carbohydrates in leaves and 20% in seed coat cup exudates. Increasing the supply of free cyclitols may increase the accumulation of their respective α-galactosides in mature seeds. Seeds with reduced RFO accumulation, but with normal to elevated concentrations of galactosyl cyclitols (including fagopyritols), have normal field emergence and are also tolerant to imbibitional chilling under laboratory conditions. Molecular structures, biosynthetic pathways, accumulation of soluble carbohydrates in response to seed-expressed mutations and the physiological role of galactosides are reviewed.

Background The novel mutant allele hsi2-4 was isolated in a genetic screen to identify Arabidopsis mutants with constitutively elevated expression of a glutathione S-transferase F8::luciferase ( GSTF8::LUC ) reporter gene in Arabidopsis. The hsi2-4 mutant harbors a point mutation that affects the plant homeodomain (PHD)-like domain in HIGH-LEVEL EXPRESSION OF SUGAR-INDUCIBLE GENE2 (HSI2)/VIVIPAROUS1/ABI3-LIKE1 (VAL1). In hsi2-4 seedlings, expression of this LUC transgene and certain endogenous seed-maturation genes is constitutively enhanced. The parental reporter line (WT LUC ) that was used for mutagenesis harbors two independent transgene loci, Kan R and Kan S . Both loci express luciferase whereas only the Kan R locus confers resistance to kanamycin. Results Here we show that both transgene loci harbor multiple tandem insertions at single sites. Luciferase expression from these sites is regulated by the HSI2 PHD-like domain, which is required for the deposition of repressive histone methylation marks (H3K27me3) at both Kan R and Kan S loci. Expression of LUC and Neomycin Phosphotransferase II transgenes is associated with dynamic changes in H3K27me3 levels, and the activation marks H3K4me3 and H3K36me3 but does not appear to involve repressive H3K9me2 marks, DNA methylation or histone deacetylation. However, hsi2-2 and hsi2-4 mutants are partially resistant to growth inhibition associated with exposure to the DNA methylation inhibitor 5-aza-2′-deoxycytidine. HSI2 is also required for the repression of a subset of regulatory and structural seed maturation genes in vegetative tissues and H3K27me3 marks associated with most of these genes are also HSI2-dependent. Conclusions These data implicate HSI2 PHD-like domain in the regulation of gene expression involving histone modifications and DNA methylation-mediated epigenetic mechanisms.

Main conclusionThe entire process of embryo development is under the tight control of various transcription factors. Together with other proteins, they act in a combinatorial manner and control distinct events during embryo development.Seed development is a complex process that proceeds through sequences of events regulated by the interplay of various genes, prominent among them being the transcription factors (TFs). The members of WOX, HD-ZIP III, ARF, and CUC families have a preferential role in embryonic patterning. While WOX TFs are required for initiating body axis, HD-ZIP III TFs and CUCs establish bilateral symmetry and SAM. And ARF5 performs a major role during embryonic root, ground tissue, and vasculature development. TFs such as LEC1, ABI3, FUS3, and LEC2 (LAFL) are considered the master regulators of seed maturation. Furthermore, several new TFs involved in seed storage reserves and dormancy have been identified in the last few years. Their association with those master regulators has been established in the model plant Arabidopsis. Also, using chromatin immunoprecipitation (ChIP) assay coupled with transcriptomics, genome-wide target genes of these master regulators have recently been proposed. Many seed-specific genes, including those encoding oleosins and albumins, have appeared as the direct target of LAFL. Also, several other TFs act downstream of LAFL TFs and perform their function during maturation. In this review, the function of different TFs in different phases of early embryogenesis and maturation is discussed in detail, including information about their genetic and molecular interactors and target genes. Such knowledge can further be leveraged to understand and manipulate the regulatory mechanisms involved in seed development. In addition, the genomics approaches and their utilization to identify TFs aiming to study embryo development are discussed.

• Temperature variation during seed set is an important modulator of seed dormancy and impacts the performance of crop seeds through effects on establishment rate. It remains unclear how changing temperature during maturation leads to dormancy and growth vigour differences in nondormant seedlings. • Here we take advantage of the large seed size in Brassica oleracea to analyse effects of temperature on individual seed tissues. • We show that warm temperature during seed maturation promotes seed germination, while removal of the endosperm from imbibed seeds abolishes temperature-driven effects on germination. We demonstrate that cool temperatures during early seed maturation lead to abscisic acid (ABA) retention specifically in the endosperm at desiccation. During this time temperature affects ABA dynamics in individual seed tissues and regulates ABA catabolism. We also show that warm-matured seeds preinduce a subset of germination-related programmes in the endosperm, whereas cold-matured seeds continue to store maturation-associated transcripts including DOG1 because of effects on mRNA degradation before quiescence, rather than because of the effect of temperature on transcription. • We propose that effects of temperature on seed vigour are explained by endospermic ABA breakdown and the divergent relationships between temperature and mRNA breakdown and between temperature, seed moisture and the glass transition.

Environmental changes during seed production are important drivers of lot‐to‐lot variation in seed behaviour and enable wild species to time their life history with seasonal cues. Temperature during seed set is the dominant environmental signal determining the depth of primary dormancy, although the mechanisms though which temperature changes impart changes in dormancy state are still only partly understood. We used molecular, genetic and biochemical techniques to examine the mechanism through which temperature variation affects Arabidopsis thaliana seed dormancy. Here we show that, in Arabidopsis, low temperatures during seed maturation result in an increase in phenylpropanoid gene expression in seeds and that this correlates with higher concentrations of seed coat procyanidins. Lower maturation temperatures cause differences in coat permeability to tetrazolium, and mutants with increased seed coat permeability and/or low procyanidin concentrations are less able to enter strongly dormant states after exposure to low temperatures during seed maturation. Our data show that maternal temperature signalling regulates seed coat properties, and this is an important pathway through which the environmental signals control primary dormancy depth.

• Seed longevity, the maintenance of viability during dry storage, is a crucial factor to preserve plant genetic resources and seed vigor. Inference of a temporal gene-regulatory network of seed maturation identified auxin signaling as a putative mechanism to induce longevity-related genes. • Using auxin-response sensors and tryptophan-dependent auxin biosynthesis mutants of Arabidopsis thaliana L., the role of auxin signaling in longevity was studied during seed maturation. • DII and DR5 sensors demonstrated that, concomitant with the acquisition of longevity, auxin signaling input and output increased and underwent a spatiotemporal redistribution, spreading throughout the embryo. Longevity of seeds of single auxin biosynthesis mutants with altered auxin signaling activity was affected in a dose–response manner depending on the level of auxin activity. Longevity-associated genes with promoters enriched in auxin response elements and the master regulator ABSCISIC ACID INSENSITIVE3 were induced by auxin in developing embryos and deregulated in auxin biosynthesis mutants. The beneficial effect of exogenous auxin during seed maturation on seed longevity was abolished in abi3-1 mutants. • These data suggest a role for auxin signaling activity in the acquisition of longevity during seed maturation.

Plants have evolved seeds to permit the survival and dispersion of their lineages by providing nutrition for embryo growth and resistance to unfavorable environmental conditions. Seed formation is a complicated process that can be roughly divided into embryogenesis and the maturation phase, characterized by accumulation of storage compound, acquisition of desiccation tolerance, arrest of growth, and acquisition of dormancy. Concerted regulation of several signaling pathways, including hormonal and metabolic signals and gene networks, is required to accomplish seed formation. Recent studies have identified the major network of genes and hormonal signals in seed development, mainly in maturation. Gibberellin (GA) and abscisic acids (ABA) are recognized as the main hormones that antagonistically regulate seed development and germination. Especially, knowledge of the molecular mechanism of ABA regulation of seed maturation, including regulation of dormancy, accumulation of storage compounds, and desiccation tolerance, has been accumulated. However, the function of ABA and GA during embryogenesis still remains elusive. In this review, we summarize the current understanding of the sophisticated molecular networks of genes and signaling of GA and ABA in the regulation of seed development from embryogenesis to maturation.