The ability of the biological control agents (BCAs) to colonize plant tissues is an important feature involved in microbe-assisted plant protection. Plant-microbe interaction research increased especially in the last decade thanks to technological revolution. Molecular methods and the development of advanced microscopic techniques allow researchers to explore gene expression and localization of beneficial microorganisms within plants. The green fluorescent protein (GFP) and its modified version, enhanced GFP (EGFP), more adapt for expression in mammalian cells and GC-rich actinomycetes like Streptomyces, have been widely used as markers to study gene expression, as well as plant-microbe interactions. Aside fluorescent protein approaches, fluorescence in situ hybridization (FISH) is another frequently used technique to visualize microbial colonization patterns and community composition by application of specific fluorescent probes. Firstly, we transformed five Streptomyces strains, which showed strong inhibition activity against Sclerotinia sclerotiorum, with the EGFP construct by the conjugation method. The conjugation efficiencies varied between the strains, but were comparable to the reference strain. The fitness of transformed strains was similar to wild-type; the transformants maintained similar sporulation, mycelium growth rate, and the ability to produce important secondary metabolites and lytic enzymes. Secondly, two transformed strains, Streptomyces cyaneus ZEA17I, and Streptomyces sp. SW06W, were used to study lettuce colonization dynamics by seed coating method. Their spatio-temporal dynamics were determined in sterile substrate. The strains were consistently recovered from lettuce rhizosphere and inner root tissues up to six weeks. Finally, the colonization pattern of lettuce by Streptomyces cyaneus ZEA17I was examined by both EGFP and FISH approaches combined with confocal laser scanning microscopy (CLSM). For FISH-CLSM analysis, universal bacteria and Streptomyces genus specific probes were used to label S. cyaneus ZEA17I. The consistent presence of the labeled strain at the lettuce root one week after sowing showed that Streptomyces spores could rapidly germinate and produce filamentous mycelium on lettuce. S. cyaneus ZEA17I was detected also on two-week-old roots, indicating the long-term survival ability of this strain in lettuce rhizosphere. Altogether, the antagonistic activity, rhizosphere and root competence showed by the Streptomyces conferred their potential to act as BCA. Further studies on the complex host-pathogen-antagonist interactions will provide additional knowledge to understand the modes and mechanisms of Streptomyces-mediated plant protection.

TAGGING BIOCONTROL STREPTOMYCES TO STUDY LETTUCE COLONIZATION / X. Chen ; supervisor: P. Cortesi ; co-supervisor: M. Saracchi ; coordinatore : D.G. Daffonchio. DIPARTIMENTO DI SCIENZE PER GLI ALIMENTI, LA NUTRIZIONE E L'AMBIENTE, 2015 Dec 17. 28. ciclo, Anno Accademico 2015. [10.13130/chen-xiaoyulong_phd2015-12-17].

TAGGING BIOCONTROL STREPTOMYCES TO STUDY LETTUCE COLONIZATION

X. Chen
2015

Abstract

The ability of the biological control agents (BCAs) to colonize plant tissues is an important feature involved in microbe-assisted plant protection. Plant-microbe interaction research increased especially in the last decade thanks to technological revolution. Molecular methods and the development of advanced microscopic techniques allow researchers to explore gene expression and localization of beneficial microorganisms within plants. The green fluorescent protein (GFP) and its modified version, enhanced GFP (EGFP), more adapt for expression in mammalian cells and GC-rich actinomycetes like Streptomyces, have been widely used as markers to study gene expression, as well as plant-microbe interactions. Aside fluorescent protein approaches, fluorescence in situ hybridization (FISH) is another frequently used technique to visualize microbial colonization patterns and community composition by application of specific fluorescent probes. Firstly, we transformed five Streptomyces strains, which showed strong inhibition activity against Sclerotinia sclerotiorum, with the EGFP construct by the conjugation method. The conjugation efficiencies varied between the strains, but were comparable to the reference strain. The fitness of transformed strains was similar to wild-type; the transformants maintained similar sporulation, mycelium growth rate, and the ability to produce important secondary metabolites and lytic enzymes. Secondly, two transformed strains, Streptomyces cyaneus ZEA17I, and Streptomyces sp. SW06W, were used to study lettuce colonization dynamics by seed coating method. Their spatio-temporal dynamics were determined in sterile substrate. The strains were consistently recovered from lettuce rhizosphere and inner root tissues up to six weeks. Finally, the colonization pattern of lettuce by Streptomyces cyaneus ZEA17I was examined by both EGFP and FISH approaches combined with confocal laser scanning microscopy (CLSM). For FISH-CLSM analysis, universal bacteria and Streptomyces genus specific probes were used to label S. cyaneus ZEA17I. The consistent presence of the labeled strain at the lettuce root one week after sowing showed that Streptomyces spores could rapidly germinate and produce filamentous mycelium on lettuce. S. cyaneus ZEA17I was detected also on two-week-old roots, indicating the long-term survival ability of this strain in lettuce rhizosphere. Altogether, the antagonistic activity, rhizosphere and root competence showed by the Streptomyces conferred their potential to act as BCA. Further studies on the complex host-pathogen-antagonist interactions will provide additional knowledge to understand the modes and mechanisms of Streptomyces-mediated plant protection.
17-dic-2015
Settore AGR/12 - Patologia Vegetale
Streptomyces; biocontrol; lettuce; EGFP (enhanced green fluorescent protein); FISH (fluorescence in situ hybridization); CLSM (confocal laser scanning microscopy); colonization
CORTESI, PAOLO
DAFFONCHIO, DANIELE GIUSEPPE
CORTESI, PAOLO
SARACCHI, MARCO
Doctoral Thesis
TAGGING BIOCONTROL STREPTOMYCES TO STUDY LETTUCE COLONIZATION / X. Chen ; supervisor: P. Cortesi ; co-supervisor: M. Saracchi ; coordinatore : D.G. Daffonchio. DIPARTIMENTO DI SCIENZE PER GLI ALIMENTI, LA NUTRIZIONE E L'AMBIENTE, 2015 Dec 17. 28. ciclo, Anno Accademico 2015. [10.13130/chen-xiaoyulong_phd2015-12-17].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2434/345187
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