Functional characterization of OsLT9 in regulating rice leaf thickness.

Leaf thickness in rice critically influences photosynthetic efficiency and yield, yet its genetic basis remains poorly understood, with few functional genes previously characterized. In this study, we employ a pangenome-wide association study (Pan-GWAS) on 302 diverse rice accessions from southern China, identifying 49 quantitative trait loci (QTLs) associated with leaf thickness. The most significant locus, qLT9, is fine-mapped to a 79 kb region on chromosome 9. Transcriptomic and genomic sequence analyses identify LOC_Os09g33480, which encodes a protein belonging to Multiple Organellar RNA Editing Factor (MORF) family, as the key candidate gene. Overexpression and complementation transgenic experiments confirm LOC_Os09g33480 (OsLT9) as the functional gene underlying qLT9, demonstrating a 24-bp Indel in its promoter correlates with the expression levels and leaf thickness. Notably, OsLT9 overexpression lines show not only thicker leaf, but also significantly enhanced photosynthetic efficiency and grain yield, establishing a link between leaf thickness modulation and yield enhancement. Population genomic analyses indicate strong selection for OsLT9 during domestication and breeding, with modern cultivars favoring thick leaf haplotype of OsLT9. This study establishes OsLT9 as a key regulator controlling leaf thickness in rice, and provides a valuable genetic resource for molecular breeding of high-yielding rice through optimization of plant architecture.