Phenotypic Identification and Fine-Mapping of the Rice Narrow-Leaf Mutant <i>nal25</i>.

Leaf morphology significantly impacts rice (<i>Oryza sativa</i> L.) plant architecture and yield. Here, we identified and characterized a novel narrow-leaf mutant, <i>nal25</i>, derived from indica rice cultivar 'Huazhan' using EMS mutagenesis. Phenotypic analyses revealed that <i>nal25</i> exhibited significantly narrower leaves, reduced plant height, increased tiller number, and notably decreased grain size, seed setting rate, and thousand-grain weight compared to the wild type. Genetic analyses demonstrated that the narrow-leaf phenotype is controlled by a single recessive nuclear gene. Through precise localization analysis, the <i>NAL25</i> gene was located within a region of approximately 103 kb on the long arm of rice chromosome 7. The sequencing results showed that the mutant <i>nal25</i> had a T to C mutation at position 173 of the heat-shock protein gene <i>LOC_Os07g09450</i> encoding the DnaJ domain in this interval, resulting in a change in amino acid 58 from leucine to proline. The qRT-PCR results showed that the expression level of <i>NAL25</i> gene decreased in the mutant. The <i>nal25</i> mutant obtained in this study exhibits stable mutant phenotypes, including dwarfism and excessive tillering, traits typically unfavorable for rice production. Nevertheless, it serves as valuable genetic material for forward genetics approaches to identify yield-related genes regulating leaf morphology and culm height. Thus, research on the <i>nal25</i> mutant advances the development of rice varieties with ideal plant architecture, thereby stabilizing yield increases and safeguarding global food security.