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.