Papers by Isabelle Debeaujon
Journal of Experimental Botany, Feb 13, 2014
NRT2.7 is a seed-specific high-affinity nitrate transporter controlling nitrate content in Arabid... more NRT2.7 is a seed-specific high-affinity nitrate transporter controlling nitrate content in Arabidopsis mature seeds. The objective of this work was to analyse further the consequences of the nrt2.7 mutation for the seed metabolism. This work describes a new phenotype for the nrt2.7-2 mutant allele in the Wassilewskija accession, which exhibited a distinctive pale-brown seed coat that is usually associated with a defect in flavonoid oxidation. Indeed, this phenotype resembled those of tt10 mutant seeds defective in the laccase-like enzyme TT10/LAC15, which is involved in the oxidative polymerization of flavonoids such as the proantocyanidins (PAs) (i.e. epicatechin monomers and PA oligomers) and flavonol glycosides. nrt2.7-2 and tt10-2 mutant seeds displayed the same higher accumulation of PAs, but were partially distinct, since flavonol glycoside accumulation was not affected in the nrt2.7-2 seeds. Moreover, measurement of in situ laccase activity excluded a possibility of the nrt2.7-2 mutation affecting the TT10 enzymic activity at the early stage of seed development. Functional complementation of the nrt2.7-2 mutant by overexpression of a full-length NRT2.7 cDNA clearly demonstrated the link between the nrt2.7 mutation and the PA phenotype. However, the PA-related phenotype of nrt2.7-2 seeds was not strictly correlated to the nitrate content of seeds. No correlation was observed when nitrate was lowered in seeds due to limited nitrate nutrition of plants or to lower nitrate storage capacity in leaves of clca mutants deficient in the vacuolar anionic channel CLCa. All together, the results highlight a hitherto-unknown function of NRT2.7 in PA accumulation/oxidation.
Recent progress in molecular genetics and omics-driven research in seed biology
Comptes Rendus. Biologies
Cells, 2021
The conjugation of sterols with a Glc moiety is catalyzed by sterol glucosyltransferases (SGTs). ... more 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. Mutant analysis had previously inferred that two Arabidopsis SGTs, UGT80A2 and UGT80B1/TT15, could have specialized roles in the production of SG in seeds, despite an overlap in their enzymatic activity. Here, we establish new roles for both enzymes in the accumulation of polysaccharides in seed coat epidermal cells (SCEs). The rhamnogalacturonan-I (RG-I) content of the inner layer of seed mucilage was higher in ugt80A2, whereas RG-I accumulation was lower in mutants of UGT80B1, with double mutant phenotypes indicating that UGT80A2 acts independently from UGT80B1. In contrast, an additive phenotype was observed in double mutants for increased gal...
Plant and Cell Physiology, 2015
Mature seeds are an ultimate physiological status that enables plants to endure extreme condition... more 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. Seeds possess two main strategies to combat these stressful conditions: protection and repair. The protective mechanism includes the formation of glassy cytoplasm to reduce cellular metabolic activities and the production of antioxidants that prevent accumulation of oxidized macromolecules during seed storage. The repair system removes damage accumulated in DNA, RNA and proteins upon seed imbibition through enzymes such as DNA glycosylase and methionine sulfoxide reductase. In addition to longevity, dormancy is also an important adaptive trait that contributes to seed lifespan. Studies in Arabidopsis have shown that the seed-specific transcription factor ABSCISIC ACID-INSENSITIVE3 (ABI3) plays a central role in ABA-mediated seed dormancy and longevity. Seed longevity largely relies on the viability of embryos. Nevertheless, characterization of mutants with altered seed coat structure and constituents has demonstrated that although the maternally derived cell layers surrounding the embryos are dead, they have a significant impact on longevity.
The Effect of a-Amanitin on the Arabidopsis Seed Proteome Highlights the Distinct Roles of Stored and Neosynthesized mRNAs during Germination 1
Plant Physiol, 2004
Plant & cell physiology, 2014
Among secondary metabolites, flavonoids are particularly important for the plant life cycle and c... more Among secondary metabolites, flavonoids are particularly important for the plant life cycle and could be beneficial for human health. The study of Arabidopsis thaliana transparent testa mutants showed that seed flavonoids are important for environmental adaptation, reactive oxygen species homeostasis, dormancy and longevity. Compared with Arabidopsis and maize (Zea mays L.), far less research has been conducted on rice (Oryza sativa L.) particularly for cultivars with non-pigmented seeds. In this study, we describe the localization, nature and relative abundance of flavonoids in mature and germinated non-pigmented Nipponbare seeds using a combination of confocal microscopy, mass spectrometry and gene expression analysis. The mature seed exclusively accumulates flavones mostly in the embryo and to a lesser extent in the pericarp/testa. Due to the variety of flavone conjugation patterns, 21 different flavones were identified, including sulfated flavones never mentioned before in cerea...
Seed Development
Plant Developmental Biology - Biotechnological Perspectives, 2009
Seed production is a key evolutionary trait of higher plants. All seed characteristics (e.g. phys... more Seed production is a key evolutionary trait of higher plants. All seed characteristics (e.g. physical and biochemical protection by the seed coat, desiccation tolerance, quiescent metabolism and accumulation of storage compounds for efficient seedling development) contribute to embryo survival and dispersion. Seed germination is tightly regulated by maternal and environmental factors such as light or temperature. Physiological and biochemical processes
Seed Development, Dormancy and Germination
seeds (Olsen, 2004). The cells of the aleurone layer remain alive at seed maturity. In mature Ara... more seeds (Olsen, 2004). The cells of the aleurone layer remain alive at seed maturity. In mature Arabidopsis seeds, a thin hyaline layer without pectin also surrounds the embryo (Debeaujon et al., 2000). The testa includes the integument(s) and the chalazal tissues (Fig. 3.1A). The testa consists of several layers of specialized cell types originating from the differentiation of ovular integuments that is triggered by fertilization. They develop from the epidermis of the ovule primordium that derives ontogenetically from the meristematic L1 cell layer (Schneitz et al., 1995). The number of ovule integuments varies depending on plant species. Most monocotyledons (e.g., wheat) and dicotyledons (e.g., Arabidopsis, bean) have two integuments (bitegmic ovules). A single integument (unitegmic ovules) is mainly found in the Rosidae, Ericales, Asteridae and Solanaceae that includes tomato, petunia and tobacco (Boesewinkel and Bouman, 1995; Angenent and Colombo, 1996). The micropyle is a pore formed by the integument(s) as an entrance for the pollen tube. The chalazal region is also an important part of the testa where the connection of the vascular tissues of the maternal funiculus to the seed ends. The scar where the funiculus was connected that remains after seed detachment is called the hilum. The differentiation of testa tissues involves important cellular changes generally ending with programed cell death (PCD). The Arabidopsis testa The Arabidopsis testa involves two integuments, the inner integument (ii) having three cell layers and the outer integument (oi) being two-layered(Schneitz et al., 1995; Beeckman et al., 2000) (Fig. 3.1). In the first few days after fertilization (daf), integument growth proceeds through both cell division and expansion (Haughn and Chaudhury, 2005). At the heart stage of embryo development, the cellular organization of testa tissues becomes evident and distinguishable (Fig. 3.1A), although further modifications are necessary to lead to the formation of the mature testa structure (Fig. 3.1B).
Advances in Botanical Research, 2012
Laccases are ubiquitous oxidases present in animals, plants, bacteria, and fungi. In plant specie... more Laccases are ubiquitous oxidases present in animals, plants, bacteria, and fungi. In plant species, they occur as large multigenic families. The involvement of peroxidases in lignification is supported by a wealth of literature data. In contrast, the role of laccases in this major plant process is less firmly established. The large number of plant laccases, which argues for a variety of functions in plant development, makes the identification of lignin-specific laccases a challenge. However, in the past decade, the development of new genetic technologies and tools has played a central role towards resolving this issue. In addition, the plant model, Arabidopsis thaliana, has recently provided novel insights about the occurrence of laccases involved in stem lignification. Information about lignin-related laccases is also available from other species, such as poplar, or other organs and tissues, such as seed coats. This review brings a short and cutting edge survey of laccases and lignification.
The Plant Journal, 1999
Mutations in the BANYULS (BAN) gene lead to precocious accumulation of anthocyanins in immature s... more Mutations in the BANYULS (BAN) gene lead to precocious accumulation of anthocyanins in immature seed coat in Arabidopsis. The ban ±1 allele has been isolated from a collection of T-DNA transformants and found to be tagged by the integrative molecule. The sequencing of wild-type and two independent mutant alleles con®rmed the identity of the gene. Analysis of the full-length cDNA sequence revealed an open reading frame encoding a 342 amino acid protein which shared strong similarities with DFR and other enzymes of the phenylpropanoid biosynthesis pathway. BAN expression was restricted to the endothelium of immature seeds at the pre-globular to early globular stages of development as predicted from the maternal inheritance of the phenotype, and therefore represents a marker for early differentiation and development of the seed coat. BAN is probably involved in a metabolic channelling between the production of anthocyanins and pro-anthocyanidins in the seed coat.
THE PLANT CELL ONLINE, 2001
In Arabidopsis, proanthocyanidins specifically accumulate in the endothelium during early seed de... more In Arabidopsis, proanthocyanidins specifically accumulate in the endothelium during early seed development. At least three TRANSPARENT TESTA (TT) genes, TT2 , TT8 , and TTG1 , are necessary for the normal expression of several flavonoid structural genes in immature seed, such as DIHYDROFLAVONOL-4-REDUCTASE and BANYULS (BAN). TT8 and TTG1 were characterized recently and found to code for a basic helix-loop-helix domain transcription factor and a WDrepeat-containing protein, respectively. Here the molecular cloning of the TT2 gene was achieved by T-DNA tagging. TT2 encoded an R2R3 MYB domain protein with high similarity to the rice OsMYB3 protein and the maize COLORLESS1 factor. A TT2-green fluorescent protein fusion protein was located mostly in the nucleus, in agreement with the regulatory function of the native TT2 protein. TT2 expression was restricted to the seed during early embryogenesis, consistent with BAN expression and the proanthocyanidin deposition profile. Finally, in gain-of-function experiments, TT2 was able to induce ectopic expression of BAN in young seedlings and roots in the presence of a functional TT8 protein. Therefore, our results strongly suggest that stringent spatial and temporal BAN expression, and thus proanthocyanidin accumulation, are determined at least partially by TT2.
The Arabidopsis TT2 Gene Encodes and R2R3 MYB Domain Protein That Acts as a Key Determinant for Proanthocyanidin Accumulation in Developing Seed
The Plant Cell, 2001
The Plant Cell, 2002
Screening for seed pigmentation phenotypes in Arabidopsis led to the isolation of three allelic y... more Screening for seed pigmentation phenotypes in Arabidopsis led to the isolation of three allelic yellow-seeded mutants, which defined the novel TRANSPARENT TESTA16 (TT16) locus. Cloning of TT16 was performed by T-DNA tagging and confirmed by genetic complementation and sequencing of two mutant alleles. TT16 encodes the ARABIDOPSIS BSIS-TER (ABS) MADS domain protein. ABS belongs to the recently identified "B-sister" (B S) clade, which contains genes of unknown function that are expressed mainly in female organs. Phylogenetic analyses using a maximum parsimony approach confirmed that TT16/ABS and related proteins form a monophyletic group. TT16 / ABS was expressed mainly in the ovule, as are the other members of the B S clade. TT16/ABS is necessary for BANYULS expression and proanthocyanidin accumulation in the endothelium of the seed coat, with the exception of the chalazal-micropylar area. In addition, mutant phenotype and ectopic expression analyses suggested that TT16/ABS also is involved in the specification of endothelial cells. Nevertheless, TT16/ABS apparently is not required for proper ovule function. We report the functional characterization of a member of the B S MADS box gene subfamily, demonstrating its involvement in endothelial cell specification as well as in the increasingly complex genetic control of flavonoid biosynthesis in the Arabidopsis seed coat.
The Plant Cell, 2000
The TRANSPARENT TESTA8 (TT8) locus is involved in the regulation of flavonoid biosynthesis in Ara... more The TRANSPARENT TESTA8 (TT8) locus is involved in the regulation of flavonoid biosynthesis in Arabidopsis. The tt8-3 allele was isolated from a T-DNA-mutagenized Arabidopsis collection and found to be tagged by an integrative molecule, thus permitting the cloning and sequencing of the TT8 gene. TT8 identity was confirmed by complementation of tt8-3 and sequence analysis of an additional allele. The TT8 gene encodes a protein that displays a basic helix-loophelix at its C terminus and represents an Arabidopsis ortholog of the maize R transcription factors. The TT8 transcript is present in developing siliques and in young seedlings. The TT8 protein is required for normal expression of two flavonoid late biosynthetic genes, namely, DIHYDROFLAVONOL 4-REDUCTASE (DFR) and BANYULS (BAN), in Arabidopsis siliques. Interestingly, TRANSPARENT TESTA GLABRA1 (TTG1) and TT2 genes also control the expression of DFR and BAN genes. Our results suggest that the TT8, TTG1, and TT2 proteins may interact to control flavonoid metabolism in the Arabidopsis seed coat.
Plant Physiology, 2000
The testa of higher plant seeds protects the embryo against adverse environmental conditions. Its... more The testa of higher plant seeds protects the embryo against adverse environmental conditions. Its role is assumed mainly by controlling germination through dormancy imposition and by limiting the detrimental activity of physical and biological agents during seed storage. To analyze the function of the testa in the model plant Arabidopsis, we compared mutants affected in testa pigmentation and/or structure for dormancy, germination, and storability. The seeds of most mutants exhibited reduced dormancy. Moreover, unlike wild-type testas, mutant testas were permeable to tetrazolium salts. These altered dormancy and tetrazolium uptake properties were related to defects in the pigmentation of the endothelium and its neighboring crushed parenchymatic layers, as determined by vanillin staining and microscopic observations. Structural aberrations such as missing layers or a modified epidermal layer in specific mutants also affected dormancy levels and permeability to tetrazolium. Both struc...
Plant Physiology, 2000
The mechanisms imposing a gibberellin (GA) requirement to promote the germination of dormant and ... more The mechanisms imposing a gibberellin (GA) requirement to promote the germination of dormant and non-dormant Arabidopsis seeds were analyzed using the GA-deficient mutant ga1, several seed coat pigmentation and structure mutants, and the abscisic acid (ABA)-deficient mutant aba1. Testa mutants, which exhibit reduced seed dormancy, were not resistant to GA biosynthesis inhibitors such as tetcyclacis and paclobutrazol, contrarily to what was found before for other non-dormant mutants in Arabidopsis. However, testa mutants were more sensitive to exogenous GAs than the wild-types in the presence of the inhibitors or when transferred to a GA-deficient background. The germination capacity of thega1-1 mutant could be integrally restored, without the help of exogenous GAs, by removing the envelopes or by transferring the mutation to a tt background (tt4 and ttg1). The double mutants still required light and chilling for dormancy breaking, which may indicate that both agents can have an effe...
Plant Physiology, 2004
To investigate the role of stored and neosynthesized mRNAs in seed germination, we examined the e... more To investigate the role of stored and neosynthesized mRNAs in seed germination, we examined the effect of α-amanitin, a transcriptional inhibitor targeting RNA polymerase II, on the germination of nondormant Arabidopsis seeds. We used transparent testa mutants, of which seed coat is highly permeable, to better ascertain that the drug can reach the embryo during seed imbibition. Even with the most permeable mutant (tt2-1), germination (radicle protrusion) occurred in the absence of transcription, while subsequent seedling growth was blocked. In contrast, germination was abolished in the presence of the translational inhibitor cycloheximide. Taken together, the results highlight the role of stored proteins and mRNAs for germination in Arabidopsis and show that in this species the potential for germination is largely programmed during the seed maturation process. The α-amanitin-resistant germination exhibited characteristic features. First, this germination was strongly slowed down, in...
Plant Methods, 2012
Background Seed transmission constitutes a major component of the parasitic cycle for several fun... more Background Seed transmission constitutes a major component of the parasitic cycle for several fungal pathogens. However, very little is known concerning fungal or plant genetic factors that impact seed transmission and mechanisms underlying this key biological trait have yet to be clarified. Such lack of available data could be probably explained by the absence of suitable model pathosystem to study plant-fungus interactions during the plant reproductive phase. Results Here we report on setting up a new pathosystem that could facilitate the study of fungal seed transmission. Reproductive organs of Arabidopsis thaliana were inoculated with Alternaria brassicicola conidia. Parameters (floral vs fruit route, seed collection date, plant and silique developmental stages) that could influence the seed transmission efficiency were tested to define optimal seed infection conditions. Microscopic observations revealed that the fungus penetrates siliques through cellular junctions, replum and ...
Plant Cell, Tissue and Organ Culture, 1993
Strategies based on the application of biotechnologies to crop improvement programmes generally r... more Strategies based on the application of biotechnologies to crop improvement programmes generally require regeneration of whole plants from cells or tissues cultivated in vitro. In Cucurbitaceae, regeneration can occur either through a caulogenic or an embryogenic developmental pathway. Reports of somatic embryogenesis have dealt with the main cultivated crops, i.e. cucumber, melon, squash and watermelon. Somatic embryogenesis and plant recovery are obtained from numerous sources including protoplasts, but the best results are observed with explants coming from seedlings, especially cotyledons and hypocotyls. The genetic constitution of mother plants also seems to play a key role in the success of embryogenesis, but few systematic studies on genotype effect have been published. Somatic embryos can exhibit developmental abnormalities, particularly when they arise from protoplast-derived cultures. Generally, data concerning embryo yield, rate of germination and plant development and characteristics of regenerated plants and their progeny, has not been provided in previous reports. The potential use of somatic embryogenesis in cucurbit breeding programmes is stressed in this review.
Plant Cell Reports, 1992
Induction of somatic embryogenesis and caulogenesis from cotyledon and leaf protoplast-derived co... more Induction of somatic embryogenesis and caulogenesis from cotyledon and leaf protoplast-derived colonies of melon (Cucumis melo L.
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Papers by Isabelle Debeaujon