Progress has been made in the study of the natural immune regulation mechanism of plants

Plants mainly rely on their natural immune systems to resist the invasion
of pathogenic microorganisms.
The pattern recognition receptor FLS2, located in the plant cell membrane, recognizes the bacterial flagellar protein-conserved peptide flg22, binds to the co-receptor kinase BAK1 and phosphorylates each other, and activates the downstream cytosolic receptor kinase BIK1
.
Activated BIK1 mediates immune responses
such as reactive oxygen species (ROS) production, calcium ion entry into cytoplasm, and stomatal closure.

To prevent excessive immune responses from causing harm to plant cells themselves, BIK1 abundance is precisely regulated
by regulatory modules.
In this regulatory module, calcium-dependent protein kinase 28 (CPK28) negatively regulates BIK1 abundance
.
Previous studies have found that CPK28 is ubiquitinated by two E3 ubiquitin ligases ATL31/6, resulting in CPK28 degradation by the proteasome (Liu et al.
, Plant Cell, 2022).

In the process of plant immune activation, CPK28 undergoes intermolecular autophosphorylation and BIK1-mediated phosphorylation, and whether the phosphorylation state of CPK28 determines the ubiquitination modification and degradation of CPK28 is unclear
.

The large team of crop design breeding at the Agricultural Resources Research Center of the Institute of Genetics and Developmental Biology, Chinese Academy of Sciences found that mutations in the Ser318 site (intermolecular autophosphorylation and BIK1-mediated phosphorylation site) or T76 site (BIK1-mediated phosphorylation site) of CPK28 led to the weakening of the interaction between CPK28 and ATL31, and reduced the ubiquitination modification of CPK28 by ATL31, thereby weakening
the degradation of CPK28 。 In addition, the study confirmed that the two CPK28 molecules can interact with each other, which may promote intermolecular autophosphorylation; The phosphorylation state of CPK28 in turn affects the interaction
between CPK28 molecules.
In summary, the phosphorylation state of CPK28 affects ATL31-mediated degradation of CPK28 protein
.
This study explores the relationship between CPK28 phosphorylation modification, ubiquitination modification and degradation, and further reveals the activation mechanism
of plant immunity.

On November 4, the findings were published in New Phytologist, titled Phosphorylation status of CPK28 affects its ubiquitination and protein stability
.
The research work was supported
by the National Natural Science Foundation of China, the Natural Science Foundation of Hebei Province and the State Key Laboratory of Plant Genomics.

The phosphorylation state of CPK28 determines its ubiquitination modification and protein stability

Source: Agricultural Resources Research Center, Institute of Genetics and Development, Chinese Academy of Sciences