Loss of ROC5 Induces Leaf Rolling with Pleiotropic Yield Penalties and Transcriptomic Shifts in Rice

ROC5, an HD-ZIP IV transcription factor, negatively regulates bulliform cell development and leaf rolling in rice (Oryza sativa L.). Its molecular partners in epidermal cell fate are well characterised, but its broader effects on agronomic performance and gene expression remain largely unexplored. We evaluated a CRISPR/Cas9-generated roc5 loss-of-function line in the Korean elite japonica cultivar 'Samkwang' over two field seasons, with comparative RNA-seq analysis of flag leaf and panicle tissues at the heading stage. The roc5 line exhibited abaxial leaf rolling; reductions in culm and panicle length, grain number per panicle, and spikelet fertility, resulted in a 32.9% yield penalty relative to the wild type. Stomatal traits were unaffected, supporting the bulliform-cell-specific action of ROC5. RNA-seq identified 196 differentially expressed genes (DEGs) in the flag leaf and 106 in the panicle, with upregulated genes predominating in both tissues. Fifty DEGs were shared and regulated in the same direction across tissues. Gene ontology (GO) enrichment revealed coordinated downregulation of metal ion transporters, including ZIP family members, and upregulation of photosystem II components in the flag leaf. These findings reveal pleiotropic consequences well beyond leaf morphology and suggest a possible link between HD-ZIP IV transcription factors, the transcriptional regulation of metal ion transport, and yield determination in rice.