Laurent Legendre and Claire Prigent-Combaret, Ecologie Microbienne, Université Lyon, France
von 14:15 bis 16:00
|Wo||KHS, Schänzlestr. 1, 79104 Freiburg|
Open to University employees
Université Lyon 1, Villeurbanne, France; CNRS, UMR5557, Ecologie Microbienne
Biosynthesis of sclareol, a diterpene natural product of high value for the fragrance industry
With its labdane carbon skeleton and its two hydroxyl groups, sclareol is a valued stating material for the hemisynthesis of numerous commercial substances such as Ambrox®, a sustainable substitute for ambregris in the fragrance industry. Most of the commercially-produced sclareol derives from clary sage (Salvia sclarea) cultivation and extraction. In this plant, sclareol mainly accumulates in essential oil-producing trichome structures that densely cover flower calices. Manool is a minor diterpene of this species and the main diterpene of related Salvia species. In order to gain knowledge on the biosynthetic pathway leading to sclareol, an EST library was constructed from clary sage calices and subjected to 454-pyrosequencing. This provided transcriptome knowledge on over 45 000 unigenes. BLAST-based analyses revealed that it contained candidate genes for all of the known biosynthetic steps of terpenes in plants from either the mevalonate cytosolic pathway or the methyerythritol phosphate chloroplastic pathway. Among them, a class of enzymes called terpene synthases is responsible for a key cyclisation step and, therefore, for the making of the complex carbon skeletons of terpenes. We cloned and functionally characterized two diterpene synthase enzymes, SsLPPS and SsSS. Both are monofunctional diterpene synthases that represent some of the first fully characterized hydroxylating diterpene synthases in angiosperms. Together, they generate the dihydroxylated labdane sclareol and the monohydroxylated labdane manool as co-product without any need for additional oxygenating enzyme activities such as cytochrome P450 monoxygenases. Knowledge on these enzymes opens the path for the development of the bioengineered production of oxygenated diterpenes.
Rhizosphere team, UMR CNRS 5557 Ecologie Microbienne, Université Lyon 1, 69622 Villeurbanne, France
Plant growth promoting properties of Azospirillum and 2,4-diacetylphloroglucinol producing Pseudomonas
Intensive cultivation of some cereals is consuming water and fertilizers, leading not only to depletion of water resources, but also to important chemical pollution of groundwater and soil. Within the rhizosphere, certain microbial populations can benefit plant by stimulating root growth, which is typically the case with Plant Growth-Promoting Rhizobacteria (PGPR) (Richardson et al., 2009 Plant Soil 321:305-339*). PGPR stimulate growth mainly (i) by enhancing nutrient availability (N fixation, P solubilisation), (ii) by increasing root ramification and elongation, which may take place via bacterial production of phytohormones, (iii) by alleviating the effects of stress in the plant, and (iv) by inhibiting the growth of phytopathogens. PGPR strains are usually categorized into two main groups: phytostimulators such as Azospirillum that are well-known for their effects on root system architecture (i.e. enhanced numbers of lateral roots and root hairs) (Bashan et al., 2010 Adv. Agron. 108:77-135), and phytoprotectors like 2,4-diacetylphloroglucinol (DAPG) producing fluorescent Pseudomonas (Couillerot et al., 2009 Let. Appl. Microbiol. 48:505-512*). These biocontrol PGPR are effective in controlling diseases such as take-all of wheat, black root rot of tobacco, by inhibiting soilborne pathogens and triggering systemic resistance pathways in plant that render the host less susceptible to pathogen infection (Weller, 2007 Phytopathology 97:250-256). But, despite this distinction, we hypothesize that DAPG-producing pseudomonads have the capacity to enhance, through an indirect fashion, the growth and development of plant, and that Azospirillum have the ability to protect the plant against phytopathogens. To address this hypothesis, we developed two strategies. First, we studied the impact of DAPG and DAPG-producing Pseudomonas on PGPR phytostimulators like Azospirillum, and evidenced that DAPG stimulates indirectly plant growth, by enhancing expression of Azospirillum’s plant beneficial functions such as the biosynthesis of indole-3-acetic acid (auxin family), thereby improving the growth of the plant (Combes-Meynet et al., 2011 MPMI 24:271-284). Second, we develop comparative genomic analyses on Azospirillum sequenced genomes to identify properties potentially involved in plant protection against phytopathogens. These two approaches evidence that DAPG-producing Pseudomonas and Azospirillum can be considered as both phytostimulators and phytoprotectors and might be useful for both promoting the growth and improving the health of plants.