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Abstract Arabidopsis thaliana (hereafter Arabidopsis) is a small plant with a fast generation time and a well-annotated genome, which makes it ideal for research labs. It is arguably the most used model species in basic plant sciences. Over the past half century, studies in Arabidopsis have generated enormous insight into fundamental principles of plant life, ranging from mechanistic molecular biology to the complexities of interacting ecosystems. Based on research in Arabidopsis, we now understand that while basic cellular metabolism is generally conserved across species, variation in specialized metabolite enzymes gives rise to complex bouquets of chemical weapons that are tightly interwoven with the environment. Understanding how these are produced, regulated, and—especially—how they are deployed remains a key research area for plant immunity. The breadth of work in Arabidopsis provides a unique window into this complicated aspect of life as a plant. We are happy to have an opportunity to share our common interest in these aspects in this review. Due to space constraints, we focus on compounds produced by Arabidopsis with demonstrated antimicrobial properties. We hope that this focus (despite our eagerness to write more) will inspire new avenues of research that will contribute to a more complete understanding of immunity. 

SUMMARY Identification of protein interactors is ideally suited for the functional characterization of small molecules. 3′,5′‐cAMP is an evolutionary ancient signaling metabolite largely uncharacterized in plants. To tap into the physiological roles of 3′,5′‐cAMP, we used a chemo‐proteomics approach, thermal proteome profiling (TPP), for the unbiased identification of 3′,5′‐cAMP protein targets. TPP measures shifts in the protein thermal stability upon ligand binding. Comprehensive proteomics analysis yielded a list of 51 proteins significantly altered in their thermal stability upon incubation with 3′,5′‐cAMP. The list contained metabolic enzymes, ribosomal subunits, translation initiation factors, and proteins associated with the regulation of plant growth such as CELL DIVISION CYCLE 48. To functionally validate obtained results, we focused on the role of 3′,5′‐cAMP in regulating the actin cytoskeleton suggested by the presence of actin among the 51 identified proteins. 3′,5′‐cAMP supplementation affected actin organization by inducing actin‐bundling. Consistent with these results, the increase in 3′,5′‐cAMP levels, obtained either by feeding or by chemical modulation of 3′,5′‐cAMP metabolism, was sufficient to partially rescue the short hypocotyl phenotype of theactin2 actin7mutant, severely compromised in actin level. The observed rescue was specific to 3′,5′‐cAMP, as demonstrated using a positional isomer 2′,3′‐cAMP, and true for the nanomolar 3′,5′‐cAMP concentrations reported for plant cells.In vitrocharacterization of the 3′,5′‐cAMP–actin pairing argues against a direct interaction between actin and 3′,5′‐cAMP. Alternative mechanisms by which 3′,5′‐cAMP would affect actin dynamics, such as by interfering with calcium signaling, are discussed. In summary, our work provides a specific resource, 3′,5′‐cAMP interactome, as well as functional insight into 3′,5′‐cAMP‐mediated regulation in plants.