Faithful pollen wall formation requires tight control of both the amplitude and duration of tapetal transcriptional activity. However, how such dynamic restraint is achieved during anther development remains poorly understood. Here, we identify a phosphorylation-dependent regulatory module in which SBI-PP2A-C1/C5 constrains the functional activity window of the tapetal transcription factor bHLH089 to safeguard male fertility. PP2A-C1 and PP2A-C5 physically associate with bHLH089 and limit its transcriptional output by reducing bHLH089 phosphorylation and nuclear retention, thereby restricting its nuclear accumulation and effective activity. Genetic analyses reveal that precise PP2A-C1/C5 dosage is critical for pollen wall integrity, as both reduced PP2A-C function and PP2A-C1/C5 overexpression disrupt tapetal transcriptional homeostasis and compromise male fertility. Mechanistically, Ser28 and Ser58 function as conserved phosphorylation-dependent determinants of bHLH089 nuclear retention and are required for PP2A-C1/C5-sensitive regulation of bHLH089 activity. Together, these findings identify a phosphatase-mediated timing mechanism that integrates transcriptional feedback with post-translational control to constrain bHLH089-driven transcriptional amplification within a self-limiting tapetal activity window required for tapetal homeostasis, pollen wall formation, and male fertility.
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