Cell Host Microbe A new mechanism of interaction between plant immune system and auxin-secreting probiotics

Written by Chang Dao | Yifan plant roots are in a complex soil environment, surrounded by numerous microorganisms.
According to the effect of bacteria on plant growth and health, they are mainly divided into pathogenic bacteria (harmful), probiotic bacteria (beneficial) and neutral Bacteria (no obvious effect) [1, 2]
.

When plants face bacteria, the first molecular response is to activate their immune system.
Host plants use receptors on the cell surface and the bacteria’s microbial-related molecular patterns (MAMPs, mainly including flagella, peptidoglycan, elongation factors, etc.
) Recognizing each other, the early stage will cause the leakage of calcium ions and the burst of reactive oxygen species (ROS), accompanied by the phosphorylation of immune-related proteins, and then the immune signal is transmitted downstream [3-7]
.

Research on the identification and activation of plant immune system in pathogenic bacteria has been more in-depth, however, there are relatively few studies on the interaction between the microbial community around the roots of healthy plants and the plant immune system.
In particular, the response of beneficial bacteria to the plant immune system needs to be further explored [ 8-10]
.

Recently, the team of Philip N.
Benfey of Duke University in the United States published a research paper entitled Plant immune system activation is necessary for efficient interaction with auxin secreting beneficial bacteria in Cell Host & Microbe, a top journal in immunology, and found that the activation of the plant immune system Helps to colonize the roots of beneficial bacteria
.

In this study, the researchers observed the colonization of wild-type Bacillus and auxin-deficient mutant strains in the roots of Arabidopsis thaliana and found that the secretion of auxin is necessary for bacteria to colonize the roots of plants; by studying the process of bacterial colonization of roots, it is activated The immune-related pathways (including flagellin, peptidoglycan, bacterial elongation factor and other mutant plant materials) confirm that synthetic auxin is a necessary condition for probiotics to participate in plant immune activities
.

In order to identify plant immune components activated by bacteria, the researchers tested the colonization of mutants and wild-type strains on Arabidopsis immune-related gene mutants
.

The results showed that bacterial secretion of auxin can antagonize the production of ROS in plants and promote root colonization.
At the same time, it was found that auxin can protect bacteria from surviving the toxicity of ROS.
Further analysis of the effect of auxin on bacterial root colonization showed that to a certain extent, Auxin affects the ability of bacteria to adhere to the root rather than the root's response to the bacteria
.

In order to clarify the mechanism by which auxin promotes root adhesion and spread, the researchers screened a series of mutant strains related to colonization (including movement, adhesion and biofilm formation), and found that auxin-induced flagella production can enhance lateral root stimulation The required root colonization is formed
.

In order to determine whether the interaction between bacterial auxin secretion and plant immunity also affects other bacteria, the researchers conducted a correlation analysis on Gram-positive bacteria that can also synthesize auxin, and the results showed that the bacterial colonization stimulated by auxin has strain specificity , Is not a universal phenomenon, and the enhancement of Bacillus colonization on plants can better protect plants from fungus infection
.

In summary, this study found that there is a feedback loop between the plant immune system and bacterial auxin secretion.
The main reason is that Bacillus polymyxa and Arthrobacter sp Immune pathway recognition
.

The research has deepened the understanding of the interaction between probiotic hormone secretion and the host immune system, and is conducive to promoting the further application of biocontrol bacteria in agricultural production
.

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1038/nrmicro.
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[10] Stringlis, IA et al.
Root transcriptional dynamics induced by beneficial rhizobacteria and microbial immune elicitors reveal signatures of adaptation to mutualists.
Plant J 93, 166-180, doi:10.
1111/tpj.
13741 (2018).
Original link: https:// /fulltext/S1931-3128(21)00421-2Pseudomonas syringae: what it takes to be a pathogen.
Nat Rev Microbiol 16, 316-328, doi:10.
1038/nrmicro.
2018.
17 (2018).
[10] Stringlis, IA et al.
Root transcriptional dynamics induced by beneficial rhizobacteria and microbial immune elicitors reveal signatures of adaptation to mutualists.
Plant J 93, 166-180, doi:10.
1111/tpj.
13741 (2018).
Original link: https:// 3128(21)00421-2Pseudomonas syringae: what it takes to be a pathogen.
Nat Rev Microbiol 16, 316-328, doi:10.
1038/nrmicro.
2018.
17 (2018).
[10] Stringlis, IA et al.
Root transcriptional dynamics induced by beneficial rhizobacteria and microbial immune elicitors reveal signatures of adaptation to mutualists.
Plant J 93, 166-180, doi:10.
1111/tpj.
13741 (2018).
Original link: https:// 3128(21)00421-2