Phosphorylation fine‐tunes ceramide synthase activity and stability to modulate sphingolipid biosynthesis and immune responses
Bibliographic record
Abstract
Ceramide synthases (CerSs) are central to sphingolipid biosynthesis and influence plant development and defense responses. However, how CerS activity is regulated in plants remains unclear. Here, we discovered that LAG ONE HOMOLOG 2 (LOH2), the sole long-chain CerS in Arabidopsis (Arabidopsis thaliana), is post-translationally regulated by the ubiquitous kinase casein kinase 2 (CK2). CK2 interacts with LOH2 and phosphorylates serine residues S289 and S291 within its C-terminal region. We mutated these two serines to alanines and expressed the resulting non-phosphorylatable LOH2 variant in transgenic plants and protoplasts. We found that phosphorylation enhances LOH2 enzymatic activity, partially by increasing its substrate-binding affinity, but concurrently promotes LOH2 polyubiquitination and degradation via the 26S proteasome without affecting its subcellular localization. Plants expressing a non-phosphorylatable LOH2 variant showed diminished cell death, reduced C16 ceramide biosynthesis and salicylic acid (SA) accumulation, and compromised resistance to the fungal toxin Fumonisin B1 and the bacterial pathogen Pseudomonas syringae. Pathogen infection induces LOH2 phosphorylation, promoting C16 ceramide accumulation, SA production, and resistance gene expression. Collectively, our findings demonstrate that CK2 fine-tunes LOH2 enzymatic activity and stability, and thus the production of long-chain ceramides through phosphorylation, thereby regulating plant development and defense responses.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".