Microtubule plus-end dynamics are tightly coupled to the turnover of the MOR1 polymerase
Bibliographic record
Abstract
ABSTRACT MOR1/XMAP215/Dis1/Stu2 family proteins function as polymerases that promote microtubule assembly through tubulin-interacting N-terminal tumor-overexpressed gene (TOG) domains. It remains unclear how the polymerase activity of these proteins is coordinated with their movement along the growing microtubule lattice. Previously, it was found that a L174F mutation in the N-terminal TOG domain of the 217 kDa Arabidopsis thaliana MICROTUBULE ORGANIZATION 1 (MOR1) protein impaired microtubule growth and shrinkage rates in a temperature-dependent manner. In this study, we used a homologous recombination strategy to generate stable transgenic lines expressing full-length MOR1 and mutant mor1-1 L174F proteins tagged with the yellow fluorescent protein YPet. When expressed in mor1 mutant backgrounds, MOR1-3xYPet showed strong association with both the growing and shrinking microtubule plus ends, consistent with its involvement in both polymerization and depolymerization. By contrast, when expressed in a wild-type background, MOR1-3xYPet was redistributed along the microtubule lattice, microtubule growth rates were reduced, and plant growth was stunted. By quantifying fluorescence recovery after photobleaching, we confirmed that MOR1 has greater affinity for the plus end than the lattice. Exploiting the FRAP technique further, we identified a positive and linear correlation between microtubule polymerization rates and MOR1 turnover at the microtubule plus end. When microtubule growth rates were reduced in the mor1-1-YPet line by shifting the temperature from 21 to 30°C and for MOR1-3xYPet under taxol treatments, MOR1’s turnover was delayed. In contrast, microtubule growth rates and MOR1 turnover were hastened at 30°C or after CRISPR/Cas9-mediated knock out of the CLASP protein. These findings support a new model whereby MOR1 has finite processivity on the microtubule, catalyzing a limited fixed number of tubulin additions before dissociation. HIGHLIGHTS MOR1 has high affinity for both growing and shrinking microtubule plus ends, consistent with a function in both polymerization and depolymerization events. MOR1 has greater affinity for microtubule plus ends than the lattice, and lattice binding associated with overexpression is detrimental to plant growth. MOR1 transiently associates with the microtubule plus end, the duration of which is tightly coupled with its polymerase activity.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| 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) | 0.001 | 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 source (direct Gemma or distilled Codex), 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".