The <scp>bHLH</scp> family <scp>NITROGEN‐REPLETION INSENSITIVE1</scp> represses nitrogen starvation‐induced responses in <i>Chlamydomonas reinhardtii</i>
Bibliographic record
Abstract
SUMMARY The use of nitrogen (N) fertilizers has contributed to a quadrupling of agricultural production. However, >50% of N fertilizers remain unabsorbed by crops and leak into the environment, demanding strategies to improve N use efficiency. To identify the regulatory mechanisms of N assimilation, we performed a genetic screen using a Chlamydomonas reinhardtii strain whose motility depends upon the transcription of nitrate reductase‐encoding NIT1 , which is upregulated in response to N starvation. A constantly swimming mutant, nitrogen repletion insensitive 1 ( nri1 ), was isolated and found to express N starvation‐induced genes in N‐replete culture. NRI1 , previously reported as NSG17 ( nitrogen starvation‐induced gene 17 ), encodes a basic helix–loop–helix (bHLH) family transcription factor homologous to BES‐interacting myc ‐like (BIM) in plants. Transcriptome analysis of N‐replete nri1 culture revealed a concerted upregulation of the genes involved in the uptake and assimilation of external N sources. Many transcription factor‐encoding genes in the bHLH and SBP families were also upregulated in nri1 culture. The DNA‐binding sites of bHLH and SBP proteins were enriched in the promoters of the upregulated genes in nri1 , suggesting that NRI1 suppresses transcriptional activators to regulate N starvation‐induced genes. Consistent with the ammonium‐insensitive gene expression pattern, N‐starved nri1 gametes could not dedifferentiate back to vegetative cells when incubated in ammonium‐containing media. Taken together, we conclude that NRI1 represses N starvation‐specific responses when sufficient N is supplied in C. reinhardtii . Further investigation of how cellular N conditions regulate NRI1 activity will unravel the elusive mechanisms by which plant cells sense and respond to N starvation.
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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 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 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".