The Arabidopsis <i>HOP2</i> Gene Has a Role in Preventing illegitimate Exchanges between Nonhomologous Chromosomes
Bibliographic record
Abstract
ABSTRACT Meiotic homologous chromosomes pair up and undergo crossing over. In many eukaryotes both intimate pairing and crossing over require the induction of double stranded breaks (DSBs) and subsequent repair via Homologous Recombination (HR). In these organisms, two key proteins are the recombinases RAD51 and DMC1. Recombinase-modulators HOP2 and MND1 have been identified as proteins that assist RAD51 and DMC1 and are needed to promote stabilized pairing. We have probed the nature of the genetic lesions seen in hop2 mutants and looked at the role of HOP2 in the fidelity of genetic exchanges. Using γH2Ax as a marker for unrepaired DSBs we found that hop2-1 and mnd1 mutants have different appearance/disappearance for DSBs than wild type, but all DSBs are repaired by mid-late pachytene. Therefore, the bridges and fragments seen from metaphase I onward are due to mis-repaired DSBs, not unrepaired ones. Studying Arabidopsis haploid meiocytes we found that wild type haploids produced the expected five univalents, but hop2-1 haploids suffered many illegitimate exchanges that were stable enough to produce bridged chromosomes during segregation. Our results suggest that HOP2 has a significant active role in preventing nonhomologous associations. We also found evidence that HOP2 plays a role in preventing illegitimate exchanges during repair of radiation-induced DSBs in rapidly dividing petal cells. Thus, HOP2 plays both a positive role in promoting homologous chromosome synapsis and a separable role in preventing nonhomologous chromosome exchanges. Possible mechanisms for this second important role are discussed. SIGNIFICANCE STATEMENT The fidelity of Homologous Recombination (HR) during meiosis is essential to the production of viable gametes and for maintaining genome integrity in vegetative cells. HOP2 is an important protein for accurate meiotic HR in plants. We find high levels of illegitimate repairs between nonhomologous chromosomes during meiosis and in irradiated petal cells in HOP2 mutants. We consider mechanisms of how this second role might be accomplished.
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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 | 0.000 | 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) | 0.002 | 0.001 |
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".