Comparison of five xylan synthesis mutants reveals new insight into the mechanisms of xylan synthesis
Bibliographic record
Abstract
Previous studies using co-expression analysis have identified a large number of genes likely to be involved in secondary cell-wall formation. However, the function of very few of these genes is known. We have studied the cell-wall phenotype of irx7, irx8 and irx9, three previously described irregular xylem (irx) mutants, and irx14 and parvus-3, which we now show also to be secondary cell-wall mutants. All five mutants, which have mutations in genes encoding putative glycosyltransferases, exhibited large decreases in xylan. In addition, all five mutants were found to have the same specific defect in xylan structure, retaining MeGlcUA but lacking GlcUA side branches. Polysaccharide analysis by carbohydrate gel electrophoresis (PACE) was used to determine the xylan structure in Arabidopsis, and revealed that side branches are added to approximately one in every eight xylose residues. Interestingly, this ratio is constant in all the lines analysed despite the wide variation in xylan content and the absence of GlcUA branches. Xylanase digestion of xylan from wild-type plants released a short oligosaccharide sequence at the reducing end of the xylan chain. MALDI-TOF MS analysis indicated that this sequence of sugars was absent in xylan from irx7, irx8 and parvus-3 mutants, but was present in irx9 and irx14. This is consistent with previous NMR analysis of xylan from irx7, irx8 and irx9, and suggests that PARVUS may be involved in the synthesis of a xylan primer whereas IRX14 may be required to synthesize the xylan backbone. This hypothesis is supported by assays showing that irx9 and irx14 are both defective in incorporation of radiolabel from UDP (14)C-xylose. This study has important implications for both our understanding of xylan biosynthesis and the functional analysis of cell-wall biosynthesis genes.
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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) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 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".