Benzoxazinoids influence rhizosphere establishment and root colonization by PGPB

• Autor(a) principal: Baatsen, Jeroen
• Data de Publicação: 2024
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: Biblioteca Digital de Teses e Dissertações da USP
• Texto Completo: https://www.teses.usp.br/teses/disponiveis/11/11137/tde-06062024-083116/
• topic: Fusarium; Fusarium; Benzoxazinoides; Benzoxazinoids; Biofilm; Biofilme; BPCP; Chemotaxis; Colonização radicular; PGPB; Quimoitaxia; Root colonization; Transciptoma; Transciptome

Benzoxazinoids (BXs) form a group of secondary metabolites produced by many plants of the grass family (Poaceae). Release and activation of BXs upon pathogen attack strongly suppresses disease of pest species and foraging of herbivorous insects in areal parts of the plant. At the same time, BXs are constitutively produced and set free in the rhizosphere predominantly during early plant development, where they affect microbial interaction. Hydroxamic acid BX derivatives such as 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA), 2,4- dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) and 2-hydroxy-4,7-dimethoxy-1,4- benzoxazin-3-one (HDMBOA) in general are more reactive but have a shorter half-life than the lactam derivatives 2-benzoxazolinone (BOA) and 6-methoxy-2-benzoxazolinone (MBOA). Regardless, MBOA is more efficient at suppressing several fungal pathogens and influences microbial rhizospheric interactions over generations of plants. Key to understanding plant-microbe symbiosis is knowledge about the means of chemical communication between symbionts, and the physiological changes those signaling molecules evoke on each symbiont. Therefore, we aimed to study the mechanisms by which an interspecies exchange of information precedes the initiation of symbiosis establishment. In order to gain more insight into these processes, we investigated how MBOA mediate root colonization by the plant growth promoting bacteria (PGPB) Azospirillum brasilense Ab-V5, Bacillus thuringiensis RZ2MS9, Pantoea agglomerans 33.1 and Pseudomonas protegens Pf-5, and the adverse effect on several fungal species of the pathogenic Fusarium. We found that bacterial response to exogenic MBOA was specific for each PGPB and dose dependent. Curiously, Fusarium strains isolated from non-BX-producing hosts were susceptible to MBOA at low doses, while maize isolated Fusarium (from a BX-producing host) was tolerant. Root colonization patterns by Ab-V5 and Pf-5 were studied in more detail, showing preference for crevices and root hairs as primary colonization sites. MBOA did not influence Pf-5 biofilm formation on Arabidopsis roots but Ab-V5 biofilm was improved. Finally, results from in vitro experiments were cross validated by transcriptomic assays on Ab-V5 where a chemotaxis regulatory protein showed a relative upregulation in 0.05 mM MBOA treatment and we could correlated the amount of differential expressed genes related to biofilm production with MBOA concentration. The Pf-5 transcriptome however, was little affected, which was consistent with previously obtained results. We conclude that MBOA in intermediate concentrations stimulates the motile form Ab-V5, while high concentrations of MBOA evoke a metabolic switch in preparation of root colonization.