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Responsible editor | Yifan plants mainly rely on the immune receptors (PRR) on the cell membrane to recognize the microbial-related molecular patterns of pathogens (MAMP, such as bacterial flagella flg22 and fungal chitin) activation mode triggered immunity (PTI), so as to obtain protection against pathogens Basic resistance.
Continuous activation of PTI will inhibit plant growth.
Therefore, the negative regulator of PTI has very important physiological functions.
On the other hand, pathogenic bacteria can secrete pathogenic factors into plant cells and cause plant susceptibility (ETS) through negative regulation of PTI.
Furthermore, plants can use intracellular immune receptors (R proteins) to sense pathogenic factors or their destructive effects, and activate effect-triggered immunity (ETI), which is mainly in the form of cell death.
The above is the classic "Z" model of plant-pathogen interaction.
For example, RIN4, the negative regulator of Arabidopsis PTI, can bind to FLS2 and inhibit its activation to prevent FLS2 from activating immunity without recognizing flg22; FLS2's recognition of flg22 can lead to phosphorylation at Ser141 of RIN4.
Release the inhibition of FLS2 and activate PTI; the pathogenic factor AvrRpm1 secreted by Pseudomonas syringae can manipulate the unknown Arabidopsis kinase to phosphorylate the Thr166 site of RIN4, thereby inhibiting the phosphorylation of Ser141 induced by flg22 and keeping RIN4 right Inhibition of FLS2 causes ETS; Arabidopsis thaliana then recognizes Thr166 phosphorylation of RIN4 through the R protein RPM1, and activates ETI.
However, what host kinase AvrRpm1 uses to phosphorylate the Thr166 site of RIN4 remains to be elucidated.
On February 2, 2021, Li Jianfeng's research group at Sun Yat-sen University published a research paper entitled The receptor-like cytoplasmic kinase CDG1 negatively regulates Arabidopsis pattern-triggered immunity and is involved in AvrRpm1-induced RIN4 Phosphorylation in The Plant Cell, revealing the The Arabidopsis receptor cytoplasmic kinase CDG1 is a negative regulator of PTI, and AvrRpm1 can induce CDG1 to phosphorylate the Thr166 site of RIN4, resulting in plant ETS.
In this study, the authors first overexpressed 23 receptor-like cytoplasmic kinase (RLCK) VII family members one by one in Arabidopsis protoplasts, and found that overexpression of CDG1 can inhibit MAPK activation triggered by flg22.
Subsequently, CDG1 overexpression or knockout plants were constructed, and the negative regulation of flg22 signal transduction by CDG1 was confirmed from the plant level.
It was also found that CDG1 was also involved in the negative regulation of chitin signal transduction.
Next, the authors found that CDG1 can interact with flg22 receptor FLS2 and chitin co-receptor CERK1, and the auto-activation caused by CDG1 overexpression can cause the degradation of FLS2 and CERK1.
Further research found that CDG1 can also interact with MEKK1 (MAPKKK8) in the MAPK cascade pathway.
Surprisingly, under the background of MEKK1 kinase inactivation, the overexpression of CDG1 will not cause the degradation of FLS2 and CERK1; on the contrary, the overexpression of MEKK1 induced by estradiol or the constitutively activated MPK4 D198G/E202A mutant can promote FLS2.
degradation.
These results indicate that the MPK4 pathway mediated by CDG1 and its downstream MEKK1 is involved in the negative feedback regulation of FLS2 stability activated by flg22.
On the other hand, the authors found that AvrRpm1 can induce CDG1 to interact with RIN4 and phosphorylate the Thr166 site of RIN4 in vitro.
In the cdg1 mutant, the phosphorylation of RIN4 Thr166 induced by AvrRpm1 and the cell death triggered by this phosphorylation were significantly reduced, suggesting that CDG1 is one of the host kinases that is manipulated by AvrRpm1 and phosphorylates the Thr166 site of RIN4.
Finally, the authors found that the expression of AvrRpm1 can also induce the degradation of FLS2.
This degradation is completely dependent on RIN4, partly on CDG1, but not on the kinase activity of MEKK1, indicating that the degradation of FLS2 regulated by CDG1 in PTI and the degradation of FLS2 regulated by AvRpm1 in ETS go through different mechanisms.
Doctoral student Yang Qiujiao of Sun Yat-sen University is the first author of the paper, and Professor Li Jianfeng is the only corresponding author.
The research was funded by a general project of the National Natural Science Foundation of China.
Paper link: https://academic.
oup.
com/plcell/advance-article/doi/10.
1093/plcell/koab033/6126474
Continuous activation of PTI will inhibit plant growth.
Therefore, the negative regulator of PTI has very important physiological functions.
On the other hand, pathogenic bacteria can secrete pathogenic factors into plant cells and cause plant susceptibility (ETS) through negative regulation of PTI.
Furthermore, plants can use intracellular immune receptors (R proteins) to sense pathogenic factors or their destructive effects, and activate effect-triggered immunity (ETI), which is mainly in the form of cell death.
The above is the classic "Z" model of plant-pathogen interaction.
For example, RIN4, the negative regulator of Arabidopsis PTI, can bind to FLS2 and inhibit its activation to prevent FLS2 from activating immunity without recognizing flg22; FLS2's recognition of flg22 can lead to phosphorylation at Ser141 of RIN4.
Release the inhibition of FLS2 and activate PTI; the pathogenic factor AvrRpm1 secreted by Pseudomonas syringae can manipulate the unknown Arabidopsis kinase to phosphorylate the Thr166 site of RIN4, thereby inhibiting the phosphorylation of Ser141 induced by flg22 and keeping RIN4 right Inhibition of FLS2 causes ETS; Arabidopsis thaliana then recognizes Thr166 phosphorylation of RIN4 through the R protein RPM1, and activates ETI.
However, what host kinase AvrRpm1 uses to phosphorylate the Thr166 site of RIN4 remains to be elucidated.
On February 2, 2021, Li Jianfeng's research group at Sun Yat-sen University published a research paper entitled The receptor-like cytoplasmic kinase CDG1 negatively regulates Arabidopsis pattern-triggered immunity and is involved in AvrRpm1-induced RIN4 Phosphorylation in The Plant Cell, revealing the The Arabidopsis receptor cytoplasmic kinase CDG1 is a negative regulator of PTI, and AvrRpm1 can induce CDG1 to phosphorylate the Thr166 site of RIN4, resulting in plant ETS.
In this study, the authors first overexpressed 23 receptor-like cytoplasmic kinase (RLCK) VII family members one by one in Arabidopsis protoplasts, and found that overexpression of CDG1 can inhibit MAPK activation triggered by flg22.
Subsequently, CDG1 overexpression or knockout plants were constructed, and the negative regulation of flg22 signal transduction by CDG1 was confirmed from the plant level.
It was also found that CDG1 was also involved in the negative regulation of chitin signal transduction.
Next, the authors found that CDG1 can interact with flg22 receptor FLS2 and chitin co-receptor CERK1, and the auto-activation caused by CDG1 overexpression can cause the degradation of FLS2 and CERK1.
Further research found that CDG1 can also interact with MEKK1 (MAPKKK8) in the MAPK cascade pathway.
Surprisingly, under the background of MEKK1 kinase inactivation, the overexpression of CDG1 will not cause the degradation of FLS2 and CERK1; on the contrary, the overexpression of MEKK1 induced by estradiol or the constitutively activated MPK4 D198G/E202A mutant can promote FLS2.
degradation.
These results indicate that the MPK4 pathway mediated by CDG1 and its downstream MEKK1 is involved in the negative feedback regulation of FLS2 stability activated by flg22.
On the other hand, the authors found that AvrRpm1 can induce CDG1 to interact with RIN4 and phosphorylate the Thr166 site of RIN4 in vitro.
In the cdg1 mutant, the phosphorylation of RIN4 Thr166 induced by AvrRpm1 and the cell death triggered by this phosphorylation were significantly reduced, suggesting that CDG1 is one of the host kinases that is manipulated by AvrRpm1 and phosphorylates the Thr166 site of RIN4.
Finally, the authors found that the expression of AvrRpm1 can also induce the degradation of FLS2.
This degradation is completely dependent on RIN4, partly on CDG1, but not on the kinase activity of MEKK1, indicating that the degradation of FLS2 regulated by CDG1 in PTI and the degradation of FLS2 regulated by AvRpm1 in ETS go through different mechanisms.
Doctoral student Yang Qiujiao of Sun Yat-sen University is the first author of the paper, and Professor Li Jianfeng is the only corresponding author.
The research was funded by a general project of the National Natural Science Foundation of China.
Paper link: https://academic.
oup.
com/plcell/advance-article/doi/10.
1093/plcell/koab033/6126474
