Abstract
Several root-colonizing bacterial species can simultaneously promote plant growth and induce systemic resistance. How these rhizobacteria modulate plant metabolism to accommodate the carbon and energy demand from these two competing processes is largely unknown. Here, we show that strains of three Paraburkholderia species, P. graminis PHS1 (Pbg), P. hospita mHSR1 (Pbh), and P. terricola mHS1 (Pbt), upon colonization of the roots of two Broccoli cultivars led to cultivar-dependent increases in biomass, changes in primary and secondary metabolism and induced resistance against the bacterial leaf pathogen Xanthomonas campestris. Strains that promoted growth led to greater accumulation of soluble sugars in the shoot and particularly fructose levels showed an increase of up to 280-fold relative to the non-treated control plants. Similarly, a number of secondary metabolites constituting chemical and structural defense, including flavonoids, hydroxycinnamates, stilbenoids, coumarins and lignins, showed greater accumulation while other resource-competing metabolite pathways were depleted. High soluble sugar generation, efficient sugar utilization, and suppression or remobilization of resource-competing metabolites potentially contributed to curb the tradeoff between the carbon and energy demanding processes induced by Paraburkholderia-Broccoli interaction. Collectively, our results provide a comprehensive and integrated view of the temporal changes in plant metabolome associated with rhizobacteria-mediated plant growth promotion and induced resistance.
Highlights
Several root-colonizing bacterial species can simultaneously promote plant growth and induce systemic resistance
We investigated the effects of root-colonizing strains of three Paraburkholderia species on the phenotypes of two Broccoli cultivars, in particular on growth and defense against the bacterial leaf pathogen Xanthomonas campestris
Our results showed common and specific signatures in both primary and secondary metabolism in the two Broccoli cultivars colonized by the strains of the Paraburkholderia species
Summary
Several root-colonizing bacterial species can simultaneously promote plant growth and induce systemic resistance How these rhizobacteria modulate plant metabolism to accommodate the carbon and energy demand from these two competing processes is largely unknown. We show that strains of three Paraburkholderia species, P. graminis PHS1 (Pbg), P. hospita mHSR1 (Pbh), and P. terricola mHS1 (Pbt), upon colonization of the roots of two Broccoli cultivars led to cultivar-dependent increases in biomass, changes in primary and secondary metabolism and induced resistance against the bacterial leaf pathogen Xanthomonas campestris. Recent studies showed that a number of rhizobacteria elicit secondary metabolite accumulation, including metabolites involved in defense[8,14,15,16,17] Such changes in plant secondary metabolism have costs associated with the biosynthesis, transport and storage of these molecules and with the competition for primary metabolites and energy needed for plant growth. To begin to identify the bacterial traits associated with plant growth promotion, we screened live cells, heat-killed cells, cell-free culture supernatant and volatile compounds of Pbg and found that for growth promotion, Broccoli requires live Pbg cells
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