BAK1 protects the receptor-like kinase BIR2 from SNIPER2a/b-mediated degradation to promote pattern-triggered immunity in Nicotiana benthamiana

Proteolysis in plant immunity

Compared with transcription and translation, protein degradation machineries can act faster and be targeted to different subcellular compartments, enabling immediate regulation of signaling events. It is therefore not surprising that proteolysis has been used extensively to control homeostasis of key regulators in different biological processes and pathways. Over the past decades, numerous studies have shown that proteolysis, where proteins are broken down to peptides or amino acids through ubiquitin-mediated degradation systems and proteases, is a key regulatory mechanism to control plant immunity output. Here, we briefly summarize the roles various proteases play during defence activation, focusing on recent findings. We also update the latest progress of ubiquitin-mediated degradation systems in modulating immunity by targeting plant membrane-localized pattern recognition receptors, intracellular nucleotide-binding domain leucine-rich repeat receptors, and downstream signaling components. Additionally, we highlight recent studies showcasing the importance of proteolysis in maintaining broad-spectrum resistance without obvious yield reduction, opening new directions for engineering elite crops that are resistant to a wide range of pathogens with high yield.

Genome-wide identification of Brassinosteroid insensitive 1-associated receptor kinase 1 genes and expression analysis in response to pathogen infection in cucumber (Cucumis sativus L.)

BACKGROUND

BAK1 (Brassinosteroid insensitive 1-associated receptor kinase 1) plays an important role in disease resistance in plants. However, the function of BAK1 family in cucumber and the decisive genes for disease-resistance remain elusive.

RESULTS

Here, we identified 27 CsBAK1s in cucumber, and classified them into five subgroups based on phylogenetic analysis and gene structure. CsBAK1s in the same subgroup shared the similar motifs, but different gene structures. Cis-elements analysis revealed that CsBAK1s might respond to various stress and growth regulation. Three segmentally duplicated pairwise genes were identified in cucumber. In addition, Ka/Ks analysis indicated that CsBAK1s were under positive selection during evolution. Tissue expression profile showed that most CsBAK1s in Subgroup II and IV showed constitutive expression, members in other subgroups showed tissue-specific expression. To further explore whether CsBAK1s were involved in the resistance to pathogens, the expression patterns of CsBAK1s to five pathogens (gummy stem blight, powdery mildew, downy mildew, grey mildew, and fusarium wilt) reveled that different CsBAK1s had specific roles in different pathogen infections. The expression of CsBAK1-14 was induced/repressed significantly by five pathogens, CsBAK1-14 might play an important role in disease resistance in cucumber.

CONCLUSIONS

27 BAK1 genes were identified in cucumber from a full perspective, which have important functions in pathogen infection. Our study provided a theoretical basis to further clarify the function of BAK1s to disease resistance in cucumber.

Deubiquitylating enzymes in Arabidopsis thaliana endocytic protein degradation

The regulation of ubiquitylation is key for plant growth and development, in which the activities of ubiquitylating enzymes as well as deubiquitylating enzymes (DUBs) determine the stability or function of the modified proteins. In contrast with ubiquitylating enzymes, there are less numbers of DUBs. DUBs can be classified into seven protein families according to the amino acid sequence of their catalytic domains. The catalytic domains of animal and plant DUB families show high homology, whereas the regions outside of the catalytic site can vary a lot. By hydrolyzing the ubiquitin molecules from ubiquitylated proteins, DUBs control ubiquitin-dependent selective protein degradation pathways such as the proteasomal-, autophagic-, and endocytic degradation pathways. In the endocytic degradation pathway, DUBs can modulate the endocytic trafficking and thus the stability of plasma membrane proteins including receptors and transporters. To date, three DUB families were shown to control the endocytic degradation pathway namely associated molecule with the SH3 domain of STAM (AMSH) 3, ubiquitin-specific protease (UBP) 12 and UBP13, and ovarian tumor protease (OTU) 11 and OTU12. In this review we will summarize the activity, molecular functions, and target protein of these DUBs and how they contribute to the environmental response of plants.