Short description
(English)
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Study of the molecular interaction between different wheat cultivars and root-associated plant-beneficial pseudomonads, focusing in particular on the impact of the plant host on the expression of important bacterial traits associated with plant health. Design of optimal cultivar-bacterium combinations for sustaining wheat growth and health in low-input agricultural production systems.
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Partners and International Organizations
(English)
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AT, BE, CH, CY, CZ, DE, DK, EE, ES, FI, FR, GR, HU, IE, IL, IS, IT, LT, LV, MK, NL, NO, PL, PT, RO, SE, SK, UK
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Abstract
(English)
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A promising strategy for improving crop productivity and health under low-input agricultural condi-tions may be the application of growth-promoting bacteria to roots. Within COST action 860, we have studied molecular interactions of cereal cultivars with root-colonising pseudomonads that sus-tain plant growth by suppressing root diseases caused by pathogenic fungi. We investigated to which extent select cereal varieties may favour the expression of relevant plant-beneficial traits in these bacteria, particularly efficient root colonisation and production of metabolites that are essential for antifungal activity. For this purpose, we examined P. fluorescens strains CHA0 and Q2-87 that are well-characterised representatives of two major genotypic groups of beneficial pseudomonads naturally present in many agricultural soils. CHA0 produces multiple potent antifungal metabolites, including diacetylphloroglucinol (DAPG), pyoluteorin, and pyrrolnitrin. Q2-87 produces only DAPG as a major antifungal compound. To monitor rhizosphere effects of cereal cultivars on the expres-sion of biosynthetic genes for these antifungal metabolites, reporter constructs based on green and red fluorescent proteins (GFP, DsRed) were used in combination with fluorescence-activated cell sorting (FACS). The DsRed variant mCherry served as an internal marker for growth and GFP si-multaneously as a reporter for antifungal gene expression within the same bacterial strain, allowing selective single-cell level analysis of plant effects. With this experimental approach, we recorded bacterial colonisation levels and antifungal gene expression on roots of a selection of wheat, spelt and triticale cultivars. FACS analysis revealed that DAPG and pyrrolnitrin gene expression was best sustained in a cereal rhizosphere, whereas the other antifungal genes were poorly expressed. When focusing on DAPG, variations in gene expression were relatively modest among the different cereal cultivars, but expression levels tended to be markedly higher on roots of spelt cultivars. Compared with P. fluorescens CHA0, strain Q2-87 exhibited significantly lower root colonisation and DAPG expression levels, suggesting that cereal-specific responses may vary among different groups of plant-beneficial pseudomonads. We also checked whether a leaf pathogen attack may further affect P. fluorescens gene expression on roots. However, only minor changes in DAPG gene expression levels could be detected following infection of wheat with the leaf pathogen Puccina, though greenhouse experiments indicated that treatment with the root inoculant CHA0 may promote resistance of wheat to some leaf pathogens. Our findings highlight subtle differences in cereal-pseudomonad interactions that depend on the inoculant, the cereal genotype and health status, and the antifungal gene. Our approach may help identify bacterium-cereal combinations that optimally sustain plant growth and resistance to root and leaf diseases under low-input conditions.
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