MEMBERS' HIGHLIGHTS

Plant-microorganism interactions is an area in which Toulouse has one of the most important concentrations of scientists worldwide. The research activities in this domain involve two symbiotic interactions (with nitrogen-fixing rhizobia bacteria and with nutrient-acquiring mycorrhizal fungi) and interactions with various fungal and bacterial plant pathogens.

During the last two months the “Plant Science Research Laboratory” http://www.lrsv.ups-tlse.fr/ and http://www2.toulouse.inra.fr/ifr40/fr/ in Toulouse where the Interbio Director’s is working, has published two important papers, one in Nature and one in Science.

Fungal lipochitooligosaccharide symbiotic signals in arbuscular mycorrhiza

Fabienne Maillet et al. NATURE | VOL 469 | 6 JANUARY 2011 | 58-64

doi:10.1038/nature09622

Arbuscular mycorrhiza (AM) is a root endosymbiosis between plants and glomeromycete fungi. It is the most widespread terrestrial plant symbiosis, improving plant uptake of water and mineral nutrients. Yet, despite its crucial role in land ecosystems, molecular mechanisms leading to its formation are just beginning to be unravelled. Recent evidence suggests that AM fungi produce diffusible symbiotic signals. Here we show that Glomus intraradices secretes symbiotic signals that are a mixture of sulphated and non-sulphated simple lipochitooligosaccharides (LCOs), which stimulate formation of AM in plant species of diverse families (Fabaceae, Asteraceae and Umbelliferae). In the legume Medicago truncatula these signals stimulate root growth and branching by the symbiotic DMI signalling pathway. These findings provide a better understanding of the evolution of signalling mechanisms involved in plant root endosymbioses and will greatly facilitate their molecular dissection. They also open the way to using these natural and very active molecules in agriculture.

http://www.nature.com/nature/journal/v469/n7328/pdf/nature09622.pdf

Signatures of Adaptation to Obligate Biotrophy in the Hyaloperonospora arabidopsidis Genome

Laura Baxter et al. Science10  | Vol. 330 no. 6010 | December 2010: | pp. 1549-1551
 DOI: 10.1126/science.1195203

Many oomycete and fungal plant pathogens are obligate biotrophs, which extract nutrients only from living plant tissue and cannot grow apart from their hosts. Although these pathogens cause substantial crop losses, little is known about the molecular basis or evolution of obligate biotrophy. Here, we report the genome sequence of the oomycete Hyaloperonospora arabidopsidis(Hpa), an obligate biotroph and natural pathogen of Arabidopsis thaliana. In comparison with genomes of related, hemibiotrophic Phytophthoraspecies, the Hpagenome exhibits dramatic reductions in genes encoding (i) RXLR effectors and other secreted pathogenicity proteins, (ii) enzymes for assimilation of inorganic nitrogen and sulfur, and (iii) proteins associated with zoospore formation and motility. These attributes comprise a genomic signature of evolution toward obligate biotrophy

http://www.sciencemag.org/content/330/6010/1549.full.pdf

These fundamental studies provide new data for promising biotechnological strategies in agriculture.