Functional specialization of TAF4b governs early prophase I entry and recombination frequency in Brassica rapa

While the core transcription factor TAF4b is known to regulate meiotic transcription and recombination in model plant Arabidopsis thaliana , its functional specialization and evolutionary dynamics remain poorly understood in paleopolyploid crops. To address this, we investigated how the unique, single-copy TAF4b gene modulates early meiotic progression and reproductive success in Brassica rapa .

We characterized multiple independent taf4b TILLING lines for fertility and meiotic behavior, then used this information to select a mutant line for further investigation using a pipeline combining whole-genome background sequencing (DNA-seq), stage-specific anther transcriptomics (RNA-seq), yeast two-hybrid assays, and quantitative cytogenetics.

Disruption of the meiosis-enriched TAF4b gene on chromosome A7 universally reduced crossover frequency and depleted HEI10 foci, triggering occasional univalent formation. Global RNA-seq and structural modeling indicate that this phenotype is driven by a precise transcriptional dysregulation and altered molecular interactions restricted to the interphase/leptotene transition.

In conclusion, TAF4b acts as a stage-specific upstream gatekeeper of the early prophase I expression program in B. rapa , thereby playing an essential, non-redundant role in its meiotic stability.