Free amino acid composition of coconut (Cocos nucifera L.) calli under somatic embryogenesis induction conditions

Au cours de cette étude, 6 acides aminés ont été suivi : proline, valine, leucine, sérine, alanine et la threonine. Les cals ont été classés en 5 groupes selon leur teneur en acides aminés et leur stade de développement morphogénétique. Cette répartition a été confirmée par une analyse discriminante et une analyse de variance. Les acides aminés se sont révélés être de bons marqueurs de l'évolution des cals vers l'embryogenèse somatique, tout au moins pour le clone L82. Cette méthode pourrait-être mise en oeuvre pour sélectionner les lignées les plus embryogènes chez le cocotie

RSF Governs Silent Chromatin Formation via Histone H2Av Replacement

Human remodeling and spacing factor (RSF) consists of a heterodimer of Rsf-1 and hSNF2H, a counterpart of Drosophila ISWI. RSF possesses not only chromatin remodeling activity but also chromatin assembly activity in vitro. While no other single factor can execute the same activities as RSF, the biological significance of RSF remained unknown. To investigate the in vivo function of RSF, we generated a mutant allele of Drosophila Rsf-1 (dRsf-1). The dRsf-1 mutant behaved as a dominant suppressor of position effect variegation. In dRsf-1 mutant, the levels of histone H3K9 dimethylation and histone H2A variant H2Av were significantly reduced in an euchromatic region juxtaposed with heterochromatin. Furthermore, using both genetic and biochemical approaches, we demonstrate that dRsf-1 interacts with H2Av and the H2Av-exchanging machinery Tip60 complex. These results suggest that RSF contributes to histone H2Av replacement in the pathway of silent chromatin formation

Deciphering the molecular basis of mycobacteria and lipoglycan recognition by the C-type lectin Dectin-2

Dectin-2 is a C-type lectin involved in the recognition of several pathogens such as Aspergillus fumigatus, Candida albicans, Schistosoma mansonii, and Mycobacterium tuberculosis that triggers Th17 immune responses. Identifying pathogen ligands and understanding the molecular basis of their recognition is one of the current challenges. Purified M. tuberculosis mannose-capped lipoarabinomannan (ManLAM) was shown to induce signaling via Dectin-2, an activity that requires the (α1 → 2)-linked mannosides forming the caps. Here, using isogenic M. tuberculosis mutant strains, we demonstrate that ManLAM is a bona fide and actually the sole ligand mediating bacilli recognition by Dectin-2, although M. tuberculosis produces a variety of cell envelope mannoconjugates, such as phosphatidyl-myo-inositol hexamannosides, lipomannan or manno(lipo)proteins, that bear (α1 → 2)-linked mannosides. In addition, we found that Dectin-2 can recognize lipoglycans from other bacterial species, such as Saccharotrix aerocolonigenes or the human opportunistic pathogen Tsukamurella paurometabola, suggesting that lipoglycans are prototypical Dectin-2 ligands. Finally, from a structure/function relationship perspective, we show, using lipoglycan variants and synthetic mannodendrimers, that dimannoside caps and multivalent interaction are required for ligand binding to and signaling via Dectin-2. Better understanding of the molecular basis of ligand recognition by Dectin-2 will pave the way for the rational design of potent adjuvants targeting this receptor

A CAPS marker to assist selection of tomato spotted wilt virus (TSWV) resistance in pepper

The hypersensitive resistance to tomato spotted wilt virus (TSWV) in pepper is determined by a single dominant gene (resistant allele: Tsw) in several Capsicum chinense genotypes. In order to facilitate the selection for this resistance, four RAPD (among 250 10-mer primers tested) were found linked to the Tsw locus using the bulked segregant analysis and 153 F2individuals. A close RAPD marker was converted into a codominant cleaved amplified polymorphic sequence (CAPS) using specific PCR primers and restriction enzymes. This CAPS marker is tightly linked to Tsw (0.9 ± 0.6 cM) and is helpful for marker-assisted selection in a wide range of genetic intercrosses. Key words: Capsicum sp., PCR marker, bulked segregant analysis, Tospovirus, resistance gene.</jats:p

Etude de l'induction de l'embryogenèse somatique chez le cocotier (Cocos nucifera L.) : analyse des protéines et des acides aminés

Afin de mieux caractériser les conditions d'initiation de l'embryogenèse somatique chez le cocotier, l'analyse des protéines et des acides aminés a été réalisée sur des cals en condition de multiplication et d'induction de l'embryogenèse. Une accumulation de protéines a été constatée entre le 15e et le 42e jour de culture. Elle est confirmée en histologie. Une protéine de faible poids moléculaire (14 KDa), apparaît progressivement, en condition d'embryogenèse, entre le 8e et le 42e jour de culture. La bande qui lui correspond diminue au 60e jour. En condition de multiplication, cette protéine reste stable. Les acides aminés pourraient aussi jouer un rôle-clé dans l'établissement de l'embryogenèse chez le cocotier. Par ailleurs, un besoin spécifique en ammonium au 15e jour de culture, a été mis en évidence pour des cals induits en embryogenès

Disease resistance gene analogs as candidates for QTLs involved in pepper-pathogen interactions

Whereas resistance genes (R-genes) governing qualitative resistance have been isolated and characterized, the biological roles of genes governing quantitative resistance (quantitave trait loci, QTLs) are still unknown. We hypothesized that genes at QTLs could share homologies with cloned R-genes. We used a PCR-based approach to isolate R-gene analogs (RGAs) with consensus primers corresponding with conserved domains of cloned R-genes: (i) the nucleotide binding site (NBS) and hydrophobic domain, and (ii) the kinase domain. PCR-amplified fragments were sequenced and mapped on a pepper intraspecific map. NBS-containing sequences of pepper, most similar to the N gene of tobacco, were classified into seven families and all mapped in a unique region covering 64 cM on the Noir chromosome. Kinase domain containing sequences and cloned R-gene homologs (Pto, Fen, Cf-2) were mapped on four different linkage groups. A QTL involved in partial resistance to cucumber mosaic virus (CMV) with an additive effect was closely linked or allelic to one NBS-type family. QTLs with epistatic effects were also detected at several RGA loci. The colocalizations between NBS-containing sequences and resistance QTLs suggest that the mechanisms of qualitative and quantitative resistance may be similar in some cases.Key words: Capsicum annuum, candidate gene, nucleotide binding site, kinase domain, quantitative trait loci.</jats:p