Cell wall integrity modulates a PHYTOCHROME-INTERACTING FACTOR (PIF) – HOOKLESS1 (HLS1) signalling module controlling apical hook formation in Arabidopsis
Bibliographic record
Abstract
Summary Etiolated seedlings of dicots form an apical hook to protect the meristems during soil emergence. Hook formation is the result of differential growth on both sides of the hypocotyl apex and is tightly controlled by environmental cues and hormones, among which auxin and gibberellins (GAs) are the main contributors. Cell expansion is tightly regulated by the cell wall, but whether and how feedback from this structure contributes to hook development is still unclear. Here we show that etiolated seedlings of the Arabidopsis thaliana quasimodo2-1 ( qua2 ) mutant, defective in pectin biosynthesis, display severe defects in apical hook formation and maintenance, accompanied by loss of asymmetric auxin maxima and differential cell expansion. Moreover, qua2 seedlings show reduced expression of HOOKLESS1 ( HLS1 ) and PHYTOCHROME-INTERACTING FACTOR 4 and 5 ( PIF4/5 ), positive regulators of hook formation, and accumulate reduced levels of the active gibberellin GA 4 . Treatment of wild-type seedlings with the cellulose inhibitor isoxaben (isx) also prevents hook development and represses HLS1 expression and PIF4 accumulation. Moreover, isx stabilizes the DELLA protein REPRESSOR OF ga1-3 (RGA), which inhibits HLS1 expression and hook formation. Exogenous GAs or HLS1 overexpression partially restore hook development in isx-treated seedlings. Notably, agar concentration in the medium restores, both in qua2 and isx-treated seedlings, hook development and WT-like levels of PIFs and HLS1. We propose that turgor-dependent signals link changes in cell wall integrity to the PIF4/5-HLS1 signalling module to repress differential cell elongation during hook formation. Significance statement Cell wall integrity modulates apical hook development through poorly understood mechanisms. We show here that, in Arabidopsis, repression of hook formation by either mutations in pectin biosynthesis or by isoxaben treatment is at least partially mediated by the downregulation of a gibberellin-controlled signalling module that comprises PIF4/5 and HLS1. Our results indicate that the signals derived from changes in the cell wall can modulate hormone-mediated pathways to control asymmetric growth during plant development.
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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".