Project description:Transcriptional changes occurring at the infection site of 2 weeks old Cabernet sauvignon grapevine cuttings infected with a wood pathogen (Phaeomoniella chlamydospora) in the presence of a root-inoculated biocontrol agent (Pythium oligandrum). Gene expression profiling was done using the Nimblegen whole genome array with 3 biological replicates of 3 pooled wood chunks harvested 0 and 14 d after treatment (pathogen infection, biocontrol agent inoculation, mock treatment).
Project description:The oomycete Pythium oligandrum is a potential biocontrol agent to control a wide range of fungal and oomycetes-caused diseases such as Pythium myriotylum-caused rhizome rot in ginger leading to reduced yields and compromised quality. Previously, P. oligandrum has been studied for its plant growth-promoting potential by auxin production and induction of disease resistance by elicitors such as oligandrin. Volatile organic compounds (VOCs) play beneficial roles in sustainable agriculture by enhancing plant growth and resistance. We investigated the contribution of P. oligandrum-produced VOCs on plant growth and disease suppression by initially using N. benthamiana plants for screening. P. oligandrum VOCs significantly enhanced tobacco seedling and plant biomass content. Screening of the individual VOCs showed that 3-octanone and hexadecane promoted the growth of tobacco seedlings. The total VOCs from P. oligandrum also enhanced the shoot and root growth of ginger plants. Transcriptomic analysis showed a higher expression of genes related to plant growth hormones, and stress responses in the leaves of ginger plants exposed to P. oligandrum VOCs. The concentrations of plant growth hormones such as auxin, zeatin, and gibberellic acid were higher in the leaves of ginger plants exposed to P. oligandrum VOCs. In a ginger disease biocontrol assay, the VOC-exposed ginger plants infected with P. myriotylum had lower levels of disease severity. We conclude that this study contributes to understanding the growth-promoting mechanisms of P. oligandrum on ginger and tobacco, priming of ginger plants against various stress and the mechanisms of action of P. oligandrum as a biocontrol agent.
Project description:The biocontrol agent Pseudomonas chlororaphis PA23 protects canola (Brassica napus) against infection by the necrotrophic fungus Sclerotinia sclerotiorum. Production of PA23 secondary metabolites is governed by a complex regulatory pathway that includes the GacA/GacS two component system, the PhzI/PhzR quorum-sensing system, and a novel LysR-type transcriptional regulator, called PtrA. Through RNA-sequencing, transcriptomic profiles of PA23-WT, two quorum sensing-deficient strains, PA23-AHL and PA23-phzR, and regulatory mutants PA23-gacA, PA23-gacS and PA23-ptrA were generated allowing elucidation of the PhzRI, Gac and PtrA regulons of P. chlororaphis PA23.
Project description:Background: The biological control agent Pseudomonas chlororaphis PA23 is effective at protecting Brassica napus (canola) from the necrotrophic fungus Sclerotinia sclerotiorum via direct antagonism. Despite the growing importance of biocontrol bacteria in plant protection from fungal pathogens, little is known about how the host plant responds to bacterial priming on the leaf surface or about changes in gene activity genome-wide in the presence and absence of S. sclerotiorum. Results: PA23 priming of mature canola plants reduced the number of lesion forming petals by 90%. Global RNA sequencing of the host pathogen interface showed a reduction in the number of genes uniquely upregulated in response to S. sclerotiorum by 16-fold when pretreated with PA23. Upstream defense-related gene patterns suggest MAMP-triggered immunity via surface receptors detecting PA23 flagellin and peptidoglycans. Although systemic acquired resistance was induced in all treatment groups, a response centered around a glycerol-3-phosphate (G3P)-mediated pathway was exclusively observed in plants treated with PA23 alone. Activation of these defense mechanisms by PA23 involved mild reactive oxygen species production as well as pronounced thylakoid membrane structures and plastoglobule formation in leaf chloroplasts. Conclusion: Further to the direct antibiosis that it exhibits towards the pathogen S. sclerotiorum, PA23 primes defense responses in the plant through the induction of unique local and systemic defense regulatory networks. This study has shed light on the potential effects of biocontrol agents applied to the plant phyllosphere. Understanding these interactions will aid in the development of biocontrol systems as a viable alternative to chemical pesticides in the protection of important crop systems. Mature canola leaf tissue treated with combinations of PA23 or S. sclerotiorum ascospores (3 treatment groups) was compared to a water treated control (all treatments done in triplicate).