The maize CMS-C fertility restorer gene ZmRf4b encodes an SPL transcription factor that represses ZmMAP1D-mediated co-translational turnover of mitochondrial toxic ATP6C protein.

ZmRf4b, an SPL transcription factor in CMS-C maize, represses ZmMAP1D promoter activity, enabling co-translational turnover that prevents ATP6C overaccumulation and restores fertility.

• Why it matters: The CMS-C/Rf system is underused in maize breeding because how the primary restorer ZmRf4b restores fertility was unclear. Clarifying this nucleus–mitochondria control is key to understanding mitochondrial protein homeostasis during restoration.
• What they did: ZmRf4b was map-cloned and functionally characterized, then linked to ZmMAP1D using DNA affinity purification sequencing and yeast two-hybrid screening. ZmRf4b directly binds the ZmMAP1D promoter as a transcriptional repressor, and lower ZmRf4b expression in the restorer line permits moderate ZmMAP1D accumulation.
• The result: Imported ZmMAP1D co-translationally removes the N-terminal methionine of ATP6C, targeting excess ATP6C for degradation and normalizing mitochondrial complex V assembly. This reduces reactive oxygen species accumulation and tapetal programmed cell death, ultimately restoring male fertility in CMS-C maize.

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