Characterization of a cinnamoyl-CoA reductase 1 (CCR1) mutant in maize: effects on lignification, fibre development, and global gene expression

Cinnamoyl-CoA reductase (CCR), which catalyses the first committed step of the lignin-specific branch of monolignol biosynthesis, has been extensively characterized in dicot species, but few data are available in monocots. By screening a Mu insertional mutant collection in maize, a mutant in the CCR1 gene was isolated named Zmccr1–. In this mutant, CCR1 gene expression is reduced to 31% of the residual wild-type level. Zmccr1– exhibited enhanced digestibility without compromising plant growth and development. Lignin analysis revealed a slight decrease in lignin content and significant changes in lignin structure. p-Hydroxyphenyl units were strongly decreased and the syringyl/guaiacyl ratio was slightly increased. At the cellular level, alterations in lignin deposition were mainly observed in the walls of the sclerenchymatic fibre cells surrounding the vascular bundles. These cell walls showed little to no staining with phloroglucinol. These histochemical changes were accompanied by an increase in sclerenchyma surface area and an alteration in cell shape. In keeping with this cell type-specific phenotype, transcriptomics performed at an early stage of plant development revealed the down-regulation of genes specifically associated with fibre wall formation. To the present authors’ knowledge, this is the first functional characterization of CCR1 in a grass species

The Embryo Surrounding Region.

There is converging evidence in maize, wheat, barley, Arabidopsis and other species that the endosperm in proximity of the embryo is cytologically different from the remaining endosperm. Gene expression restricted to this embryo surrounding region (ESR) reinforces the notion of a specialized endosperm domain at least in maize and Arabidopsis. The ESR is a dynamic structure that is set apart prior to cellularisation and starts to disappear with the onset of reserve accumulation in the developing seed. During later developmental stages it is frequently succeeded by a liquid filled space around the embryo. While the cytological characteristics of the regions surrounding the embryo are quite similar between the species analyzed, their functional equivalence has not yet been established. Possible functions of the ESR include nutrition or defense of the embryo as well as signaling between the embryo and the endosperm

NMR metabolomic analysis of maize kernels: characterization of a novel allele of Brittle2

International audienc

Cantharellus garnierii sp. nov., une nouvelle chanterelle des maquis miniers nikélifères de Nouvelle-Calédonie

Cantharellus garnierii sp. nov. est décrit à partir de sept récoltes provenant des maquis miniers nickélifères de Nouvelle-Calédonie. Il est signalé comme associé à Acacia spirorbis, Casuarina coltina et Nothofagus balancae au sein d'un cortège assez classique et diversifié de champignons ectomycorhiziens comprenant, entre autres, les genres Russula, Lactarius, Inocybe, Suillus, Boletus, Cantharellus... Ce taxon est caractérisé par la taille moyenne de ses carpophores, qui sont d'un jaune à jaune orangé uniforme, sa croissance le plus souvent fasciculée, sur des sols nickélifères ultrabasiques, ses spores de taille moyenne, son médiostrate relativement différencié, et enfin ses hyphes bouclées à paroi distinctement épaissie au niveau de l'épicutis. Aucune autre espèce décrite au niveau mondial ne se rapproche de C. garnierii. (Résumé d'auteur

Construction and characterisation of a BAC library from Arabidopsis halleri: evaluation of physical mapping based on conserved synteny with A. thaliana.

We constructed and characterized the .rst large-insert DNA BAC library for Arabidopsis halleri, a close relative of Arabidopsis thaliana. Double size selection of high molecular weight DNA was performed to increase the average insert size. The BAC library consists of 6128 clones of which 87% have an insert size above 125 kb. Organellar DNA contamination is estimated to 1.4%. The coverage of the library is equivalent to 4.5 times the haploid genome (250 Mb), indicating the library is suitable for almost any application. We explored the possibility of generating a physical map of A. halleri using the high conserved synteny existing between this species and A. thaliana. A set of unigenes separated by 50 kb in a 850 kb region of A. thaliana chromosome II was used to probe the library. The A. halleri BAC clones isolated with these probeswere grouped into two contigs. Analysis of BAC-end sequences revealed that the two A. halleri genomic contigs were highly colinear with the A. thaliana genome. Therefore, the exploitation of the conserved synteny existing between the two species will greatly facilitate the construction of a raw full physical map of A. halleri

Transcriptional and Metabolic Adjustments in ADP-Glucose pyrophosphorylase -deficient bt2 Maize kernels

International audienceDuring the cloning of monogenic recessive mutations responsible for a defective kernel phenotype in a Mutator-induced Zea mays mutant collection, we isolated a new mutant allele in Brittle2 (Bt2), which codes for the small subunit of ADP-glucose pyrophosphorylase (AGPase), a key enzyme in starch synthesis. Reverse transcription-polymerase chain reaction experiments with gene-specific primers confirmed a predominant expression of Bt2 in endosperm, of Agpsemzm in embryo, and of Agpslzm in leaf, but also revealed considerable additional expression in various tissues for all three genes. Bt2a, the classical transcript coding for a cytoplasmic isoform, was almost exclusively expressed in the developing endosperm, whereas Bt2b, an alternative transcript coding for a plastidial isoform, was expressed in almost all tissues tested with a pattern very similar to that of Agpslzm. The phenotypic analysis showed that, at 30 d after pollination (DAP), mutant kernels were plumper than wild-type kernels, that the onset of kernel collapse took place between 31 and 35 DAP, and that the number of starch grains was greatly reduced in the mutant endosperm but not the mutant embryo. A comparative transcriptome analysis of wild-type and bt2-H2328 kernels at middevelopment (35 DAP) with the 18K GeneChip Maize Genome Array led to the conclusion that the lack of Bt2-encoded AGPase triggers large-scale changes on the transcriptional level that concern mainly genes involved in carbohydrate or amino acid metabolic pathways. Principal component analysis of 1H nuclear magnetic resonance metabolic profiles confirmed the impact of the bt2-H2328 mutation on these pathways and revealed that the bt2-H2328 mutation did not only affect the endosperm, but also the embryo at the metabolic level. These data suggest that, in the bt2-H2328 endosperms, regulatory networks are activated that redirect excess carbon into alternative biosynthetic pathways (amino acid synthesis) or into other tissues (embryo)

Importance of ectomycorrhizal fungi in ecological restoration of mining sites in New Caledonia, Koniambo Massif

The Koniambo Massif located in the north west of New Caledonia, is mainly composed of peridotite and serpentinite. It constitutes a large nickel deposit (NiO 0,1 to 5%) currently prospected by two mining companies (Falconbridge S.A. and SMSP). The main purpose of this study is to identify native plant/fungus couples adapted to ecological restoration issues. The study consists in a toposequencial analysis of the plant formations, formed of endemic species, and the associated ectomycorrhizal fungi, along a gradient. Four plant formations (1 to 4) were identified along the sequence from a talweg (700m) to a plateau (900m). Formation 1 is characterised by a humid dense forest dominated by Nothofagus (Fagaceae) with a high plant and ectomycorrhizal fungus diversity. Formation 2 is characterised by a shrubby maquis dominated by Tristaniopsis calobuxus and T. guillainii (Myrtaceae). For the first time, these species are described as ectomycorrhizal. Moreover, in this maquis the fungal mycelium forms the matrix for the loose iron nodules (1 to 5 mm) forming the soil. Formation 3 is characterised by a sparse herbaceous maquis dominated by Costularia spp. (Cyperaceae) and Codia montan (Cunoniaceae). (Texte intégral

Mycorrhizal symbioses : their potential for soil rehabillitation and ecological restoration

In New Caledonia, nickel mining activities have drastic impacts on a rich but particularly fragile environment. Mining companies are more and more concerned with the need to restore the degraded sites, in adverse edaphic conditions. Symbioses, both nitrogen-fixing and mycorrhizal, are known to play key roles in these processes in allowing the plant nutrition with major elements like N and P, in facilitating access and use of water, in stabilizing the soils through hyphal mats and possibly buffering metal toxicity. Over 30 years of field trials, a range of plants species have been identified as good candidates for revegetalisation and ecological restoration. About 38 genera, from 20 botanical families have thus been identified by Jaffré and Pelletier (1992). To optimise the use of these plants in ecological restoration, we explored their mycorrhizal status within their natural ecosystems and characterized their fungal partners. The aim of this work is to present the particular potential of some of the candidate plants in early revegetation steps, in compatibility with their natural environmental conditions. Among the 20 botanical families, almost half (9) have been reported as including ectomycorrhizal species, which is a quite huge rate compared to the rate of ectomycorrhization among plants. For 3 families, no reports have been found on their mycorrhizal status. Arbuscular associations have been reported for 17 families, of which 2 exhibits myconodules. The characteristics of these differents associations will be presented. (Texte intégral