Christine Le Jeune

Assessing the mycorrhization level in plant roots is essential to study the effect of arbuscular mycorrhizal fungi (AMF) on plant physiological responses. Common methods used to quantify the mycorrhization of roots are based on microscopic visualization of stained fungal structures within the cortical cells. While this method is readily accessible, it remains time-consuming and does not allow checking of the symbiosis vitality. The aim of this work is thus to develop an efficient method for assessing the intensity and vitality of mycorrhiza associated with grapevine through gene expression analyses by RT-qPCR. To this end, grapevine plants were inoculated with the AMF Rhizophagus irregularis (Ri). The relationship between mycorrhization level, assessed by microscopy, and expression of several fungus and grapevine genes involved in the symbiosis was investigated. In AMF-inoculated plants, transcript amounts of fungal constitutively-expressed genes Ri18S, RiTEF1α and RiαTub were signi...

Medium-chain fatty acids (octanoic and decanoic acids) are well known as fermentation inhibitors. During must fermentation, the toxicity of these fatty acids is enhanced by ethanol and low pH, which favors their entrance in the cell, resulting in a decrease of internal pH. We present here the characterization of the mechanisms involved in the establishment of the resistance to these fatty acids. The analysis of the transcriptome response to the exposure to octanoic and decanoic acids revealed that two partially overlapping mechanisms are activated; both responses share many genes with an oxidative stress response, but some key genes were activated differentially. The transcriptome response to octanoic acid stress can be described mainly as a weak acid response, and it involves Pdr12p as the main transporter. The phenotypic analysis of knocked-out strains confirmed the role of the Pdr12p transporter under the control of WAR1 but also revealed the involvement of the Tpo1p m ajor f aci...

We investigated the effects of the arbuscular mycorrhizal fungus (AMF) Funneliformis mosseae on the growth and root architecture of plantlets of the grape rootstock 41B MGt under hydroponic conditions, and analyzed the concomitant expression of putative mycorrhizal-specific phosphate transporter 1 (PHT1) genes. In vitro propagated plantlets were acclimatized to ex vitro culture before AMF inoculation and grown under low phosphate (Pi) nutrition conditions during 6 weeks. Grape roots could be efficiently colonized by F. mosseae in this culture system, as shown by high mycorrhization frequency and intensity. The presence of many arbuscules in the cortex was coupled with high-level expression of two PHT1 genes in grape roots. These two very similar genes, named VvPht1-1 and VvPht1-2, present P1BS and MYCS regulatory motifs in their promoter, consistent with a specific role in the mycorrhizal pathway of Pi uptake. Although AMF inoculation significantly increased shoot growth, no effect ...

Leuconostoc oenos is involved in malolactic fermentation occurring during wine-making. An increasing number of wines are being inoculated with malolactic starters to control the process, and the identification and differentiation of selected strains are now indispensable both for quality control of production and for commercial purposes. In the present work we evaluated the potential use of the intergenic regions of three L. oenos strains for their differentiation. The three 16S/23S rRNA intergenic spacers were amplified in vitro by PCR, and sequences were compared. The spacer sequence was highly conserved in all strains. Inside this spacer, a tRNA-Ala gene containing an 18-bp sequence stretch which is conserved in all tRNA genes was discovered. This sequence, together with random primers, was used for characterization of ten L. oenos strains by PCR.

(1) UMR1131 Santé de la Vigne et Qualité du Vin, INRA, Université Louis Pasteur de Strasbourg, Colmar - France (2) LVBE, Université de Haute Alsace, 33 rue de Herrlisheim, BP 50568, 68008 Colmar Cedex – France. Phone : 33(0)389203136 - claude.erny@uha.fr ...

Considered as a sister species of Saccharomyces cerevisiae, Saccharomyces uvarum is, to a lesser extent, an interesting species for fundamental and applied research studies. Despite its potential interest as a new gene pool for fermenting agents, the intraspecific molecular genetic diversity of this species is still poorly investigated. In this study, we report the use of 9 microsatellite markers to describe S. uvarum genetic diversity and population structure among 108 isolates from various geographical and substrate origins (wine, cider, natural sources). Our combined microsatellite markers set allowed differentiating 89 genotypes. In contrast to S. cerevisiae genetic diversity, wild and human origin isolates were intertwined. Seventy five % of strains were proven to be homozygotes and estimated heterozygosity suggests a selfing rate above 0.95 for the different population tested here. From this point of view, the S. uvarum life cycle appears to be more closely related to S. parad...

Methods and Results: During three successive years, must was collected at different stages of the winemaking process and fermented in the laboratory or in the cellar. Saccharomyces yeasts were sampled at the beginning and at the end of the fermentations. Saccharomyces cerevisiae clones were genetically characterized by inter-δ PCR. Non-S. cerevisiae clones were identified as Saccharomyces uvarum by PCR-RFLP on MET2 gene and characterized at the strain level by karyotyping. The composition of the Saccharomyces population in the vineyard, after ...