[Show abstract][Hide abstract] ABSTRACT: The expression of the FATTY ACID ELONGATION1 genes was characterised to provide insight into the regulation of very long chain fatty acid (VLCFA) biosynthesis in Brassica napus embryos. Each of the two rapeseed homoeologous genes (Bn-FAE1.1 and Bn-FAE1.2) encoding isozymes of 3-keto-acylCoA synthase, a subunit of the cytoplasmic acyl-CoA elongase complex that controls the production of elongated fatty acids, are expressed predominantly in developing seeds. The proximal regions of the Bn-FAE1.1 and Bn-FAE1.2 promoters possess strong sequence identity suggesting that transcriptional control of expression is mediated by this region which contains putative cis-elements characteristic of those found in the promoters of genes expressed in embryo and endosperm. Histochemical staining of rapeseed lines expressing Bn-FAE1.1 promoter:reporter gene fusions revealed a strong expression in the embryo cotyledon and axis throughout the maturation phase. Quantitative analyses revealed the region, -331 to -149, exerts a major control on cotyledon specific expression and the level of expression. A second region, -640 to -475, acts positively to enhance expression levels and extends expression of Bn-FAE1.1 into the axis and hypocotyl but also acts negatively to repress expression in the root meristem. The expression of the Bn-FAE1.1 gene was not restricted to the seed but was also detected in the vascular tissues of germinating seedlings and mature plants in the fascicular cambium tissue present in roots, stem and leaf petiole. We propose that Bn-FAE1.1 expression in vascular tissue may contribute VLCFA for barrier lipid synthesis and reflects the ancestral function of FAE1 encoded 3-keto-acylCoA synthase.
[Show abstract][Hide abstract] ABSTRACT: Cette revue est consacrée à un bilan des apports de la biologie moléculaire dans le domaine de l'information génétique contenue dans le noyau des plantes. L'organisation générale des molécules d'ADN nucléaire des plantes est décrite en montrant la part importante que jouent les séquences répétées. Plusieurs types de séquences, actuellement relativement bien caractérisées, comme les gènes codant pour tes ARNr, les ADN satellites, les transposons et les gènes codant pour des protéines, sont analysés du point de vue de leur structure fine, de leur expression éventuelle, de leur évolution et de l'usage que l'on peut faire des sondes clonées correspondantes.
[Show abstract][Hide abstract] ABSTRACT: Rice genome sequencing has made it possible to establish a catalogue of its similar to 35,000 genes and of its transposable elements. This genome is both a reference and a tool for discovering gene functions, understanding its general organisation and for progressing in our knowledge of other cereal genomes. Development of next generation sequencing technologies has revolutionized analysis of the biodiversity of both cultivated varieties and related wild species. It has considerably boosted the analysis of the evolution of the Oryza genus, as well as of other cereals. It provides a fantastic genotyping tool and opens avenues for isolating and characterizing an ever-increasing number of important genes, some of which are already manipulated in breeding programmes.
[Show abstract][Hide abstract] ABSTRACT: Restriction maps for rRNA genes of the three cultivated diploid species Brassica nigra, B. oleracea, and B. campestris are described using the rDNA map of radish as a standard. rDNA subunit heterogeneity similar to that found in radish was observed in the Brassica species, thus resulting in complex hybridization patterns. Brassica campestris could be distinguished from the other two Brassica diploids by the absence of the EcoRI site E3 in the rDNA subunits in almost all the accessions tested, and by its smaller external intergenic spacer. Two radish probes covering specific regions of the rDNA subunit as well as two other heterologous probes permitted the assignment of specific fragments to coding and intergenic spacer regions. Amphidiploid species B. napus and B. juncea had rDNA profiles reflecting the combination of EcoRI fragments observed in their parental species. A series of alien addition lines disclosed rDNA regions on two chromosomes in the B. oleracea genome, distinguished by syntenic associations to other markers and by specific intergenic spacer fragment.Key words: rDNA, polyploidy, cole crops, Cruciferae, alien addition lines.
[Show abstract][Hide abstract] ABSTRACT: Programmed cell death (PCD) has a key role in defence and development of all multicellular organisms. In plants, there is a large gap in our knowledge of the molecular machinery involved at the various stages of PCD, especially the early steps. Here, we identify kiss of death (KOD) encoding a 25-amino-acid peptide that activates a PCD pathway in Arabidopsis thaliana. Two mutant alleles of KOD exhibited a reduced PCD of the suspensor, a single file of cells that support embryo development, and a reduced PCD of root hairs after a 55°C heat shock. KOD expression was found to be inducible by biotic and abiotic stresses. Furthermore, KOD expression was sufficient to cause death in leaves or seedlings and to activate caspase-like activities. In addition, KOD-induced PCD required light in leaves and was repressed by the PCD-suppressor genes AtBax inhibitor 1 and p35. KOD expression resulted in depolarization of the mitochondrial membrane, placing KOD above mitochondria dysfunction, an early step in plant PCD. A KOD∷GFP fusion, however, localized in the cytosol of cells and not mitochondria.
The EMBO Journal 02/2011; 30(6):1173-83. DOI:10.1038/emboj.2011.14 · 10.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The leucine-rich repeat class of receptor-like kinase (LRR-RLKs) encoding genes represents the largest family of putative receptor genes in the Arabidopsis thaliana genome. However, very little is known about the range of biological process that they control. We present in this paper the functional characterization of RLK7 that has all the structural features of a receptor-like kinase of the plant-specific LRR type. To this end, we identified and characterized three independent T-DNA insertion mutants, constructed lines carrying truncated versions of this putative receptor, one lacking the cytoplasmic kinase domain (RLK7Δkin) and the other one lacking 14 LRR repeats (RLK7ΔLRR) and generated RLK7 overexpressing lines. We thus provide evidences that RLK7 is involved in the control of germination speed and the tolerance to oxidant stress. First, consistent with the expression kinetics of the RLK7 gene in the seeds, we found that all three mutants showed a delay in germination, whereas the overexpressors, RLK7Δkin and RLK7ΔLRR lines displayed a phenotype of more precocious germination. Second, a non-hypothesis driven proteomic approach revealed that in the seedlings of the three T-DNA insertion lines, four enzymes directly or indirectly involved in reactive oxygen species detoxification, were significantly less abundant. Consistent with this finding, the three mutants were less tolerant than the wild type to a hydrogen peroxide treatment, whereas the overexpressors, RLK7Δkin and RLK7ΔLRR lines presented the opposite phenotype.
[Show abstract][Hide abstract] ABSTRACT: Improvements in technology have rapidly changed the field of DNA sequencing. These improvements are boosted by bio-medical research. Plant science has benefited from this breakthrough, and a number of plant genomes are now available, new biological questions can be approached and new breeding strategies can be designed. The first part of this review aims to briefly describe the principles of the new sequencing methods, many of which are already used in plant laboratories. The second part summarizes the state of plant genome sequencing and illustrates the achievements in the last few years. Although already impressive, these results represent only the beginning of a new genomic era in plant science. Finally we describe some of the exciting discoveries in the structure and evolution of plant genomes made possible by genome sequencing in terms of biodiversity, genome expression and epigenetic regulations. All of these findings have already influenced plant breeding and biodiversity protection. Finally we discuss current trends, challenges and perspectives.
[Show abstract][Hide abstract] ABSTRACT: In higher plants, lysophosphatidic acid acyltransferase (LPAAT), located in the cytoplasmic endomembrane compartment, plays an essential role in the synthesis of phosphatidic acid, a key intermediate in the biosynthesis of membrane phospholipids in all tissues and storage lipids in developing seeds. In order to assess the contribution of LPAATs to the synthesis of storage lipids, we have characterized two microsomal LPAAT isozymes, the products of homoeologous genes that are expressed in rapeseed (Brassica napus). DNA sequence homologies, complementation of a bacterial LPAAT-deficient mutant, and enzymatic properties confirmed that each of two cDNAs isolated from a Brassica napus immature embryo library encoded a functional LPAAT possessing the properties of a eukaryotic pathway enzyme. Analyses in planta revealed differences in the expression of the two genes, one of which was detected in all rapeseed tissues and during silique and seed development, whereas the expression of the second gene was restricted predominantly to siliques and developing seeds. Expression of each rapeseed LPAAT isozyme in Arabidopsis (Arabidopsis thaliana) resulted in the production of seeds characterized by a greater lipid content and seed mass. These results support the hypothesis that increasing the expression of glycerolipid acyltransferases in seeds leads to a greater flux of intermediates through the Kennedy pathway and results in enhanced triacylglycerol accumulation.
[Show abstract][Hide abstract] ABSTRACT: In Asian cultivated rice (Oryza sativa L.), aroma is one of the most valuable traits in grain quality and 2-ACP is the main volatile compound contributing to the characteristic popcorn-like odour of aromatic rices. Although the major locus for grain fragrance (frg gene) has been described recently in Basmati rice, this gene has not been characterised in true japonica varieties and molecular information available on the genetic diversity and evolutionary origin of this gene among the different varieties is still limited. Here we report on characterisation of the frg gene in the Azucena variety, one of the few aromatic japonica cultivars. We used a RIL population from a cross between Azucena and IR64, a non-aromatic indica, the reference genomic sequence of Nipponbare (japonica) and 93-11 (indica) as well as an Azucena BAC library, to identify the major fragance gene in Azucena. We thus identified a betaine aldehyde dehydrogenase gene, badh2, as the candidate locus responsible for aroma, which presented exactly the same mutation as that identified in Basmati and Jasmine-like rices. Comparative genomic analyses showed very high sequence conservation between Azucena and Nipponbare BADH2, and a MITE was identified in the promotor region of the BADH2 allele in 93-11. The badh2 mutation and MITE were surveyed in a representative rice collection, including traditional aromatic and non-aromatic rice varieties, and strongly suggested a monophylogenetic origin of this badh2 mutation in Asian cultivated rices. Altogether these new data are discussed here in the light of current hypotheses on the origin of rice genetic diversity.
[Show abstract][Hide abstract] ABSTRACT: An inverse genetic approach was used to gain insight into the role of AP2/ERF-type transcription factors genes during plant development in Arabidopsis thaliana. Here we show that the expression pattern of AtERF38, which is, among the organs tested, more intensively expressed in mature siliques and floral stems, is closely associated with tissues that undergo secondary cell wall modifications. Firstly, public microarray data sets analysis indicates that AtERF38 is coregulated with several genes involved in secondary wall thickening. Secondly, this was experimentally confirmed in different types of cells expressing a Pro(AtERF38)::GUS fusion: histochemical analysis revealed strong and specific GUS activity in outer integument cells of mature seeds, endodermal cells of the roots in the primary developmental stage and some sclerified cells of mature inflorescence stems. All of these cells are known or shown here to be characterized by a reinforced wall. The latter, which have not been well characterized to date in Arabidopsis and may be suberized, could benefit of the use of AtERF38 as a specific marker. We were not able to detect any phenotype in an insertion line in which ectopic expression of AtERF38 is caused by the insertion of a T-DNA in its promoter. Nevertheless, AtERF28 may be considered as a candidate regulator of secondary wall metabolism in particular cell types that are not reinforced by the typical deposition of lignin and cellulose, but that have at least in common accumulation of suberin-like lipid polyesters in their walls.
[Show abstract][Hide abstract] ABSTRACT: We analyzed the Arabidopsis thaliana genome sequence to detect Late Embryogenesis Abundant (LEA) protein genes, using as reference sequences proteins related to LEAs previously described in cotton or which present similar characteristics. We selected 50 genes representing nine groups. Most of the encoded predicted proteins are small and contain repeated domains that are often specific to a unique LEA group. Comparison of these domains indicates that proteins with classical group 5 motifs are related to group 3 proteins and also gives information on the possible history of these repetitions. Chromosomal gene locations reveal that several LEA genes result from whole genome duplications (WGD) and that 14 are organized in direct tandem repeats. Expression of 45 of these genes was tested in different plant organs, as well as in response to ABA and in mutants (such as abi3, abi5, lec2 and fus3) altered in their response to ABA or in seed maturation. The results demonstrate that several so-called LEA genes are expressed in vegetative tissues in the absence of any abiotic stress, that LEA genes from the same group do not present identical expression profile and, finally, that regulation of LEA genes with apparently similar expression patterns does not systematically involve the same regulatory pathway.
[Show abstract][Hide abstract] ABSTRACT: The effects of viral infection involve concomitant plant gene variations and cellular changes. A simple system is required to assess the complexity of host responses to viral infection. The genome of the Rice yellow mottle virus (RYMV) is a single-stranded RNA with a simple organisation. It is the most well-known monocotyledon virus model. Several studies on its biology, structure and phylogeography have provided a suitable background for further genetic studies. 12 rice chromosome sequences are now available and provide strong support for genomic studies, particularly physical mapping and gene identification.
The present data, obtained through the cDNA-AFLP technique, demonstrate differential responses to RYMV of two different rice cultivars, i.e. susceptible IR64 (Oryza sativa indica), and partially resistant Azucena (O. s. japonica). This RNA profiling provides a new original dataset that will enable us to gain greater insight into the RYMV/rice interaction and the specificity of the host response. Using the SIM4 subroutine, we took the intron/exon structure of the gene into account and mapped 281 RYMV stress responsive (RSR) transcripts on 12 rice chromosomes corresponding to 234 RSR genes. We also mapped previously identified deregulated proteins and genes involved in partial resistance and thus constructed the first global physical map of the RYMV/rice interaction. RSR transcripts on rice chromosomes 4 and 10 were found to be not randomly distributed. Seven genes were identified in the susceptible and partially resistant cultivars, and transcripts were colocalized for these seven genes in both cultivars. During virus infection, many concomitant plant gene expression changes may be associated with host changes caused by the infection process, general stress or defence responses. We noted that some genes (e.g. ABC transporters) were regulated throughout the kinetics of infection and differentiated susceptible and partially resistant hosts.
We enhanced the first RYMV/rice interaction map by combining information from the present study and previous studies on proteins and ESTs regulated during RYMV infection, thus providing a more comprehensive view on genes related to plant responses. This combined map provides a new tool for exploring molecular mechanisms underlying the RYMV/rice interaction.
[Show abstract][Hide abstract] ABSTRACT: The grass family comprises the most important cereal crops and is a good system for studying, with comparative genomics, mechanisms of evolution, speciation, and domestication. Here, we identified and characterized the evolution of shared duplications in the rice (Oryza sativa) and wheat (Triticum aestivum) genomes by comparing 42,654 rice gene sequences with 6426 mapped wheat ESTs using improved sequence alignment criteria and statistical analysis. Intraspecific comparisons identified 29 interchromosomal duplications covering 72% of the rice genome and 10 duplication blocks covering 67.5% of the wheat genome. Using the same methodology, we assessed orthologous relationships between the two genomes and detected 13 blocks of colinearity that represent 83.1 and 90.4% of the rice and wheat genomes, respectively. Integration of the intraspecific duplications data with colinearity relationships revealed seven duplicated segments conserved at orthologous positions. A detailed analysis of the length, composition, and divergence time of these duplications and comparisons with sorghum (Sorghum bicolor) and maize (Zea mays) indicated common and lineage-specific patterns of conservation between the different genomes. This allowed us to propose a model in which the grass genomes have evolved from a common ancestor with a basic number of five chromosomes through a series of whole genome and segmental duplications, chromosome fusions, and translocations.
The Plant Cell 02/2008; 20(1):11-24. DOI:10.1105/tpc.107.056309 · 9.58 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The green lineage is reportedly 1,500 million years old, evolving shortly after the endosymbiosis event that gave rise to early photosynthetic eukaryotes. In this study, we unveil the complete genome sequence of an ancient member of this lineage, the unicellular green alga Ostreococcus tauri (Prasinophyceae). This cosmopolitan marine primary producer is the world's smallest free-living eukaryote known to date. Features likely reflecting optimization of environmentally relevant pathways, including resource acquisition, unusual photosynthesis apparatus, and genes potentially involved in C(4) photosynthesis, were observed, as was downsizing of many gene families. Overall, the 12.56-Mb nuclear genome has an extremely high gene density, in part because of extensive reduction of intergenic regions and other forms of compaction such as gene fusion. However, the genome is structurally complex. It exhibits previously unobserved levels of heterogeneity for a eukaryote. Two chromosomes differ structurally from the other eighteen. Both have a significantly biased G+C content, and, remarkably, they contain the majority of transposable elements. Many chromosome 2 genes also have unique codon usage and splicing, but phylogenetic analysis and composition do not support alien gene origin. In contrast, most chromosome 19 genes show no similarity to green lineage genes and a large number of them are specialized in cell surface processes. Taken together, the complete genome sequence, unusual features, and downsized gene families, make O. tauri an ideal model system for research on eukaryotic genome evolution, including chromosome specialization and green lineage ancestry.
Proceedings of the National Academy of Sciences 09/2006; 103(31):11647-52. DOI:10.1073/pnas.0604795103 · 9.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Brassica napus-B. nigra addition lines were previously created using the variety ‘Darmor’ as the oilseed rape genetic background. Two isozyme loci and 46 RAPD markers were added on five different B. nigra chromosomes. The oilseed rape variety used was highly susceptible to blackleg at the cotyledon stage and only the addition of chromosome 4 gave the same level of blackleg resistance as B. nigra. This resistance was efficient whatever the isolates used. A significant effect on the development of stem canker under field conditions was observed only for the line carrying chromosome 4 which was more resistant than the susceptible control. The potential effects of two other chromosomes have to be confirmed. F1 hybrids obtained by crosses between two highly susceptible lines and the monosomic addition line carrying chromosome 4 were examined under field conditions. No effect of the oilseed rape genetic background on the expression of resistance was detected. The introduction of this resistance and mapping of the gene(s) into oilseed rape varieties are discussed.
[Show abstract][Hide abstract] ABSTRACT: Accurate DNA replication is one of the most important events in the life of a cell. To perform this task, the cell utilizes several DNA polymerase complexes. We investigated the role of DNA polymerase epsilon during gametophyte and seed development using forward and reverse genetic approaches. In Arabidopsis, the catalytic subunit of this complex is encoded by two genes, AtPOL2a and AtPOL2b, whereas the second largest regulatory subunit AtDPB2 is present as a unique complete copy. Disruption of AtPOL2a or AtDPB2 resulted in a sporophytic embryo-defective phenotype, whilst mutations in AtPOL2b produced no visible effects. Loss of AtDPB2 function resulted in a severe reduction in nuclear divisions, both in the embryo and in the endosperm. Mutations in AtPOL2a allowed several rounds of mitosis to proceed, often with aberrant planes of division. Moreover, AtDPB2 was not expressed during development of the female gametophyte, which requires three post-meiotic nuclear divisions. Since a consensus binding site for E2F transcription factors was identified in the promoter region of both genes, the promoter-reporter fusion technique was used to show that luciferase activity was increased at specific phases of the cell cycle in synchronized tobacco BY-2 cells. Our results support the idea that fertilization may utilize the mechanisms of cell cycle transcriptional regulation of genes to reactivate the divisions of the oosphere and central cell.
The Plant Journal 11/2005; 44(2):223-36. DOI:10.1111/j.1365-313X.2005.02521.x · 6.82 Impact Factor