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

Lin Zhu,Haiming Duan,Songhua Wang,Xiaomin Lu

doi:10.52586/4966

Abstract

Background: Foliar pathogen infection can induce the enrichment of beneficial microbial consortia in plant rhizosphere, but the mechanism for enhanced plant resistance is unclear. Methods: We investigated the effects of foliar pathogen infection on bacterial communities in maize rhizosphere using high throughput sequencing. Results: Maize plants grown in non-sterilized soils displayed stronger defense against the foliar pathogen Setosphaeria turcica than those in sterilized soils. Foliar pathogen infection further triggered the shift in the structure and composition of rhizosphere bacterial communities. The pathogen-infected plants specially promoted rhizosphere colonization of several bacterial taxa. The Pseudomonas genus increased in the rhizosphere after pathogen infection. Other bacterial genera such as Chitinophaga and Flavobacterium were also greatly enriched in the rhizosphere of pathogen-infected plants. Furthermore, the enriched bacterial species were isolated and were shown to interact synergistically to promote biofilm formation. Although both the Chitinophaga and Flavobacterium species did not induce plant defense, the Pseudomonas species markedly increased the resistance of plants against S. turcica. Furthermore, the consortium consisting of the Pseudomonas, Chitinophaga and Flavobacterium species (CONpcf) conferred long-acting disease resistance of maize plants as compared to the individual Pseudomonas species. Furthermore, the inoculation with the CONpcf significantly induced a marked increase in the levels of DIMBOA in maize leaves, indicating that the consortium-induced increases of DIMBOA levels partially contributed to enhancing disease resistance of plants. Conclusions: Foliar infection of maize plants by S. turcica specifically recruited a group of beneficial rhizosphere bacteria, which conferred enhanced plant defense against pathogen infection. This study provided important evidence that above-ground pathogen infection participated in the mediation of below-ground microbiome for regulating plant defense systems.

Highlights

During long-term evolution, plants have developed intricate innate immune systems against diverse pathogen attacks
We assessed the impacts of the enriched bacterial species on disease resistance of maize plants. Interactions among these bacterial species were further examined. By combination of these investigations, we examined how S. turcica-induced changes of rhizosphere microbiome and enrichment of specific bacterial species conferred the enhanced resistance of maize plants against foliar pathogen infection
To examine whether foliar pathogen challenge induced a shift in the rhizosphere microbiome, the changes of microbial communities and plant phenotypes were monitored over a period of 6 weeks after S. turcica infection (Fig. 1a)

Summary

Introduction

During long-term evolution, plants have developed intricate innate immune systems against diverse pathogen attacks. Plants can increase the pathogen defense-related ability by sensing various biotic elicitors such as pathogen-derived molecules and beneficial microbe-released chemical signals [1, 2]. The rhizobacteriainduced ISR responses are widely present in various plant species, conferring the increased broad-spectrum resistance against pathogenic microbes such as viruses, bacteria and fungi [5,6,7,8]. The defense responses of plants triggered by rhizobacteria are not associated with direct activation of defense-related pathways, but precisely perceive bacteriaderived elicitors to provoke more efficient defense actions against pathogen infection [9]. Beneficial rhizobacteria can prime the entire plants to enhance defense against diverse pathogens via the mechanism of ISR, which is dependent on the jasmonic acid (JA)/ethylene (ET)-signaling pathways [2, 3, 5, 6]. A growing body of evidence indicates a pivotal role of root-associated microbiome including enormous rhizosphere microbes in inducing ISR in plants [10, 11]

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Discussion

Conclusion