An ancient plant immune switch works differently than expected
Dou R, Castel B, Tanney CAS, Miguel VN, Bredow M
Plant Signaling
The disease resistance mechanisms protecting your tomatoes and roses were fine-tuned over hundreds of millions of years, and this study shows one key safety switch didn't even do its modern job in some of the earliest land plants.
Plants have an internal alarm system that ramps up defenses when pathogens attack, but too much alarm can hurt the plant, so a protein called CPK28 normally acts as a brake. Researchers tested this brake system in a liverwort, an ancient and simple plant, and found that even though the same molecular parts exist, they don't actually control the immune brake the way they do in flowering plants like Arabidopsis. This suggests the fine-tuning of plant immunity was refined later in evolution, after plants moved from mosses and liverworts to more complex vascular plants.
Key Findings
MpCPK28 in the liverwort Marchantia polymorpha phosphorylates MpPUB20e, which can ubiquitinate the BIK1 ortholog MpPBLa for proteasomal degradation, paralleling the Arabidopsis system.
Unlike angiosperm cpk28 mutants, Marchantia Mpcpk28 mutants showed no enhanced immune-triggered reactive oxygen species production or increased pathogen resistance against two tested pathogens.
Transgenic MpCPK28 restored function in Arabidopsis cpk28-1 mutants, showing latent functional conservation, but the key regulatory residue Thr122 (equivalent to AtPUB25/26's Thr95/94) had no functional role in MpPUB20e.
chevron_right Technical Summary
Scientists compared an immune-regulating protein in a simple liverwort to its counterpart in flowering plants and found that while the molecular machinery is conserved, its actual job in controlling immune responses evolved later, appearing only in more advanced plant lineages.
Abstract Preview
Original paper
Divergent Roles of CPK28 in Immune Homeostasis Across Land Plants.
Calcium-dependent protein kinases decode cellular calcium transients and play diverse roles in plant growth and stress responses. In Arabidopsis thaliana, AtCPK28 contributes to immune homeostasis ...
open_in_new Read full abstractAbstract copyright held by the original publisher.
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Marchantia is a genus of liverworts in the family Marchantiaceae and the order Marchantiales. The genus was named by French botanist Jean Marchant after his father. The widespread species Marchantia polymorpha has had its genome sequenced and is an incipient model organism.