Pseudomonas fluorescens MZ05 Enhances Resistance against Setosphaeria turcica by Mediating Benzoxazinoid Metabolism in the Maize Inbred Line Anke35

Abstract

Beneficial rhizobacteria can inhibit foliar pathogen infection by activation of defense responses, yet it the mechanisms of rhizobacteria-induced disease resistance remain largely unknown. Here, inoculation of susceptible maize plants with Pseudomonas fluorescens MZ05 significantly reduced disease occurrence caused by the leaf pathogen Setosphaeria turcica. Gene expression profiles of MZ05-inoculated plants were investigated by RNA-sequencing analyses, showing that several differentially expressed genes were positively associated with the metabolic processes of benzoxazinoids. Accordantly, the inoculation with P. fluorescens MZ05 resulted in a significant increase in the levels of 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one (DIMBOA) in the maize leaves. Furthermore, pre-inoculation with P. fluorescens MZ05 enhanced the transcription of two defense-related marked genes PAL and PR2a, as well as BX2 and GLU2, which are involved in DIMBOA biosynthesis, in pathogen-infected leaves. Defense responses in the inoculated plants were also greatly stronger and quicker than that in non-inoculated plants after pathogen attacks. However, virus-mediated silencing of BX2 or GLU2 remarkably attenuated the MZ05-induced effects, as evidenced by more disease occurrence and lower transcription of PAL and PR2a. Collectively, these findings indicated that the MZ05-induced increases of DIMBOA levels participated in the mediation of priming, which was the key mechanism in the rhizobacteria-induced host resistance.

Foliar pathogen-induced assemblage of beneficial rhizosphere consortia increases plant defense against Setosphaeria turcica

“…High accumulation of DIMBOA greatly elevates the ability of plants to withstand the invasion of diverse pathogens [25]. It is increasingly recognized that beneficial soil microorganisms such as Pseudomonas fluorescens and arbuscular mycorrhizal fungus (AMF) can induce the biosynthesis of DIMBOA in leaves, which contributes to increased resistance of maize plants against pathogens including Rhizoctonia solani and Setosphaeria turcica [26,27]. Mounting evidence has indicated that biofilm formation is essential for root colonization by beneficial soil bacteria [12,28].…”

“…Bacteria-forming biofilms containing exopolysaccharides hold bacterial communities together, which help them colonize the host rhizosphere [12]. Many studies have demonstrated that there is a threshold level for root colonizing bacteria to trigger ISR of host plants against microbial pathogens [4,5,11,26]. In nature, different bacteria species are able to interact synergistically in the formation of biofilms and enhance the ability of plants to inhibit pathogen infection [12].…”

Social networking in crop plants: Wired and wireless cross‐plant communications

“…DIMBOA‐treated plants recruit specific bacterial families and species such as Pseudomonas putida , thereby increasing plant resistance to several stresses (Neal & Ton, 2013). P. fluorescens increases DIMBOA and primed resistance against the fungal pathogen Setosphaeria turcica in maize (Zhou, Ma, Lu, Zhu, & Yan, 2020). The populations of bacterial plant pathogens such as Xanthomonadaceae and Agrobacterium tumefaciens decreased in benzoxazinoid‐treated plants (Cotton et al, 2019; Kudjordjie et al, 2019).…”

Social networking in crop plants: Wire and wireless cross-phytobiome communications

“…DIMBOA-treated plants recruit specific bacterial families and species such asPseudomonas putida , thereby increasing plant resistance to several stresses (Neal & Ton, 2013). P. fluorescens increases DIMBOA and primed resistance against the fungal pathogenSetosphaeria turcica in maize (Zhou, Ma, Lu, Zhu & Yan, 2020). The populations of bacterial plant pathogens such as Xanthomonadaceae and Agrobacterium tumefaciens decreased in benzoxazinoid-treated plants (Cotton et al , 2019, Kudjordjie et al , 2019.…”