Biochemical data documenting variations in mucilage polysaccharides in a range of glycosyltransferase mutants.

During Arabidopsis seed coat development, copious amounts of mucilage polysaccharides are produced in the epidermal cells. When hydrated on imbibition, these polysaccharides expand and are released to encapsulate the seed as a two-layered hydrogel. Polysaccharides are synthesized from UDP-sugars by glycosyltransferases (GTs) and several GTs, with differing activities, have been identified that contribute to mucilage polysaccharide synthesis.

Sterol Glucosyltransferases Tailor Polysaccharide Accumulation in Arabidopsis Seed Coat Epidermal Cells.

The conjugation of sterols with a Glc moiety is catalyzed by sterol glucosyltransferases (SGTs). A portion of the resulting steryl glucosides (SG) are then esterified with a long-chain fatty acid to form acyl-SG (ASG). SG and ASG are prevalent components of plant cellular membranes and influence their organization and functional properties.

Transport of UDP-rhamnose by URGT2, URGT4, and URGT6 modulates rhamnogalacturonan-I length.

Rhamnogalacturonan-I biosynthesis occurs in the lumen of the Golgi apparatus, a compartment where UDP-Rhamnose and UDP-Galacturonic Acid are the main substrates for synthesis of the backbone polymer of pectin. Recent studies showed that UDP-Rha is transported from the cytosol into the Golgi apparatus by a family of six UDP-rhamnose/UDP-galactose transporters (URGT1-6). In this study, analysis of adherent and soluble mucilage (SM) of Arabidopsis thaliana seeds revealed distinct roles of URGT2, URGT4, and URGT6 in mucilage biosynthesis.

Datasets of seed mucilage traits for Arabidopsis thaliana natural accessions with atypical outer mucilage.

The seeds of Arabidopsis thaliana become encapsulated by a layer of mucilage when imbibed. This polysaccharide-rich hydrogel is constituted of two layers, an outer layer that can be easily extracted with water and an inner layer that must be examined in situ in order to study its properties and structure in a non-destructive manner or disintegrated through hydrolysis or physical means in order to analyze its constituents. Mucilage production is an adaptive trait and we have exploited 19 natural accessions previously found to have atypical and varied outer mucilage characteristics.

Ageing beautifully: can the benefits of seed priming be separated from a reduced lifespan trade-off?

Germination performance is affected following seed exposure to a combination of temperature fluctuations and cycles of hydration and dehydration. This has long been exploited in a seed technology termed priming, which increases germination speed and seedling vigour, but these benefits have often been associated with effects on seed lifespan, or longevity, with conflicting evidence for positive and negative effects. Seed longevity is a key seed trait influencing not only the storage of commercial stocks but also in situ and ex situ seed conservation.

Lost in Translation: Physiological Roles of Stored mRNAs in Seed Germination.

Seeds characteristics such as germination ability, dormancy, and storability/longevity are important traits in agriculture, and various genes have been identified that are involved in its regulation at the transcriptional and post-transcriptional level. A particularity of mature dry seeds is a special mechanism that allows them to accumulate more than 10,000 mRNAs during seed maturation and use them as templates to synthesize proteins during germination. Some of these stored mRNAs are also referred to as long-lived mRNAs because they remain translatable even after seeds have been exposed to long-term stressful conditions.

Polysaccharide Structures in the Outer Mucilage of Seeds Visualized by AFM.

Evidence is presented that the polysaccharide rhamnogalacturonan I (RGI) can be biosynthesized in remarkably organized branched configurations and surprisingly long versions and can self-assemble into a plethora of structures. AFM imaging has been applied to study the outer mucilage obtained from wild-type (WT) and mutant ( and ) seeds. For WT mucilage, ordered, multichain structures of the polysaccharide RGI were observed, with a helical twist visible in favorable circumstances.

Natural Variation Reveals a Key Role for Rhamnogalacturonan I in Seed Outer Mucilage and Underlying Genes.

On imbibition, Arabidopsis () seeds release polysaccharides from their epidermal cells that form a two-layered hydrogel, termed mucilage. Analysis of a publicly available data set of outer seed mucilage traits of over 300 accessions showed little natural variation in composition. This mucilage is almost exclusively made up of rhamnogalacturonan I (RGI), highlighting the importance of this pectin for outer mucilage function.

Composition and physicochemical properties of outer mucilage from seeds of Arabidopsis natural accessions.

(Arabidopsis) seeds are myxospermous and release two layers of mucilage on imbibition. The outer layer can be extracted with water facilitating the analysis of its major constituent, polysaccharides. The composition and properties of outer mucilage have been determined for 306 natural accessions and six control genotypes to generate a data set comprising six traits measured in four biological replicates for each.

Emerging Functions for Cell Wall Polysaccharides Accumulated during Eudicot Seed Development.

The formation of seeds is a reproductive strategy in higher plants that enables the dispersal of offspring through time and space. Eudicot seeds comprise three main components, the embryo, the endosperm and the seed coat, where the coordinated development of each is important for the correct formation of the mature seed. In addition, the seed coat protects the quiescent progeny and can provide transport mechanisms.

Seed coats as an alternative molecular factory: thinking outside the box.

Seed coats as commodities. Seed coats play important roles in the protection of the embryo from biological attack and physical damage by the environment as well as dispersion strategies. A significant part of the energy devoted by the mother plant to seed production is channeled into the production of the cell layers and metabolites that surround the embryo.

Sticking to cellulose: exploiting Arabidopsis seed coat mucilage to understand cellulose biosynthesis and cell wall polysaccharide interactions.

The cell wall defines the shape of cells and ultimately plant architecture. It provides mechanical resistance to osmotic pressure while still being malleable and allowing cells to grow and divide. These properties are determined by the different components of the wall and the interactions between them.

Dissecting Seed Mucilage Adherence Mediated by FEI2 and SOS5.

The plant cell wall is held together by the interactions between four major components: cellulose, pectin, hemicellulose, and proteins. Mucilage is a powerful model system to study the interactions between these components as it is formed of polysaccharides that are deposited in the apoplast of seed coat epidermal cells during seed development. When seeds are hydrated, these polysaccharides expand rapidly out of the apoplastic pocket, and form an adherent halo of mucilage around the seed.

Extensive Natural Variation in Arabidopsis Seed Mucilage Structure.

Hydrated Arabidopsis thaliana seeds are coated by a gelatinous layer called mucilage, which is mainly composed of cell wall polysaccharides. Since mucilage is rich in pectin, its architecture can be visualized with the ruthenium red (RR) dye. We screened the seeds of around 280 Arabidopsis natural accessions for variation in mucilage structure, and identified a large number of novel variants that differed from the Col-0 wild-type.

Dissection of Arabidopsis NCED9 promoter regulatory regions reveals a role for ABA synthesized in embryos in the regulation of GA-dependent seed germination.

Nine-cis-epoxycarotenoid dioxygenase (NCED) catalyzes the key step of abscisic acid (ABA) biosynthesis. There are five genes encoding NCED in Arabidopsis, which differentially regulate ABA biosynthesis in a spatiotemporal manner in response to endogenous and environmental stimuli. Previous studies have shown that NCED9 is expressed in testa and embryos during seed development.

Xylans Provide the Structural Driving Force for Mucilage Adhesion to the Arabidopsis Seed Coat.

Arabidopsis (Arabidopsis thaliana) seed coat epidermal cells produce large amounts of mucilage that is released upon imbibition. This mucilage is structured into two domains: an outer diffuse layer that can be easily removed by agitation and an inner layer that remains attached to the outer seed coat. Both layers are composed primarily of pectic rhamnogalacturonan I (RG-I), the inner layer also containing rays of cellulose that extend from the top of each columella.

Xyloglucan Metabolism Differentially Impacts the Cell Wall Characteristics of the Endosperm and Embryo during Arabidopsis Seed Germination.

Cell wall remodeling is an essential mechanism for the regulation of plant growth and architecture, and xyloglucans (XyGs), the major hemicellulose, are often considered as spacers of cellulose microfibrils during growth. In the seed, the activity of cell wall enzymes plays a critical role in germination by enabling embryo cell expansion leading to radicle protrusion, as well as endosperm weakening prior to its rupture. A screen for Arabidopsis (Arabidopsis thaliana) mutants affected in the hormonal control of germination identified a mutant, xyl1, able to germinate on paclobutrazol, an inhibitor of gibberellin biosynthesis.

Staying Alive: Molecular Aspects of Seed Longevity.

Mature seeds are an ultimate physiological status that enables plants to endure extreme conditions such as high and low temperature, freezing and desiccation. Seed longevity, the period over which seed remains viable, is an important trait not only for plant adaptation to changing environments, but also, for example, for agriculture and conservation of biodiversity. Reduction of seed longevity is often associated with oxidation of cellular macromolecules such as nucleic acids, proteins and lipids.

MUCILAGE-RELATED10 Produces Galactoglucomannan That Maintains Pectin and Cellulose Architecture in Arabidopsis Seed Mucilage.

Plants invest a lot of their resources into the production of an extracellular matrix built of polysaccharides. While the composition of the cell wall is relatively well characterized, the functions of the individual polymers and the enzymes that catalyze their biosynthesis remain poorly understood. We exploited the Arabidopsis (Arabidopsis thaliana) seed coat epidermis (SCE) to study cell wall synthesis.

The ABA-deficiency suppressor locus HAS2 encodes the PPR protein LOI1/MEF11 involved in mitochondrial RNA editing.

The hot ABA-deficiency suppressor2 (has2) mutation increases drought tolerance and the ABA sensitivity of stomata closure and seed germination. Here we report that the HAS2 locus encodes the mitochondrial editing factor11 (MEF11), also known as lovastatin insensitive1. has2/mef11 mutants exhibited phenotypes very similar to the ABA-hypersensitive mutant, hai1-1 pp2ca-1 hab1-1 abi1-2, which is impaired in four genes encoding type 2C protein phosphatases (PP2C) that act as upstream negative regulators of the ABA signaling cascade.

Local evolution of seed flotation in Arabidopsis.

Arabidopsis seeds rapidly release hydrophilic polysaccharides from the seed coat on imbibition. These form a heavy mucilage layer around the seed that makes it sink in water. Fourteen natural Arabidopsis variants from central Asia and Scandinavia were identified with seeds that have modified mucilage release and float.

Understanding polysaccharide production and properties using seed coat mutants: future perspectives for the exploitation of natural variants.

Background: The epidermal cells of the seed coat of certain species accumulate polysaccharides during seed development for cell wall reinforcement or release on imbibition to form mucilage. Seed-coat epidermal cells show natural variation in their structure and mucilage production, which could explain the diverse ecophysiological roles proposed for the latter. Arabidopsis mucilage mutants have proved to be an important tool for the identification of genes involved in the production of seed-coat polysaccharides.

PECTIN METHYLESTERASE INHIBITOR6 promotes Arabidopsis mucilage release by limiting methylesterification of homogalacturonan in seed coat epidermal cells.

Imbibed seeds of the Arabidopsis thaliana accession Djarly are affected in mucilage release from seed coat epidermal cells. The impaired locus was identified as a pectin methylesterase inhibitor gene, PECTIN METHYLESTERASE INHIBITOR6 (PMEI6), specifically expressed in seed coat epidermal cells at the time when mucilage polysaccharides are accumulated. This spatio-temporal regulation appears to be modulated by GLABRA2 and LEUNIG HOMOLOG/MUCILAGE MODIFIED1, as expression of PMEI6 is reduced in mutants of these transcription regulators.

Epoxycarotenoid cleavage by NCED5 fine-tunes ABA accumulation and affects seed dormancy and drought tolerance with other NCED family members.

Carotenoid cleavage, catalyzed by the 9-cis-epoxycarotenoid dioxygenase (NCED) constitutes a key step in the regulation of ABA biosynthesis. In Arabidopsis, this enzyme is encoded by five genes. NCED3 has been shown to play a major role in the regulation of ABA synthesis in response to water deficit, whereas NCED6 and NCED9 have been shown to be essential for the ABA production in the embryo and endosperm that imposes dormancy.

CESA5 is required for the synthesis of cellulose with a role in structuring the adherent mucilage of Arabidopsis seeds.

Imbibed Arabidopsis (Arabidopsis thaliana) seeds are encapsulated by mucilage that is formed of hydrated polysaccharides released from seed coat epidermal cells. The mucilage is structured with water-soluble and adherent layers, with cellulose present uniquely in an inner domain of the latter. Using a reverse-genetic approach to identify the cellulose synthases (CESAs) that produce mucilage cellulose, cesa5 mutants were shown to be required for the correct formation of these layers.