Abstract: Leaf rolling is an important agronomic trait in rice, influenced by both environmental and genetic factors. In this study, we identified a mutant with a slightly adaxial leaf-rolling phenotype in rice, named curly leaf 2-1 (cul2-1). The cul2-1 mutation reduces the size of bulliform cells, thereby leading to the upward-curled leaf phenotype. In addition, cul2-1 exhibited compromised agronomic performance and reduced grain yield. Using a map-based cloning approach, a G-to-A mutation was identified in cul2-1. CUL2 encodes a seryl-tRNA synthetase in the Class Ⅱ subfamily. The CUL2 protein features a conserved aminoacyl-tRNA synthetase Ⅱ (AaRSⅡ) domain composed of six β-sheets. A cysteine-to-tyrosine single amino acid substitution within this domain leads to loss of its function. CUL2 is globally expressed and the encoded protein is localized in the cytoplasm. CUL2 homologs are conserved across major crops and Arabidopsis. CUL2 regulates leaf rolling by modulating transcript levels of key genes involved in bulliform cell development, including ROC1, ROC8, RL14, REL2, ACL1, and ACL2. Collectively, our findings demonstrate that CUL2 plays an essential role in normal leaf development and grain yield formation in rice, providing new insights into the molecular mechanisms underlying leaf morphology and crop productivity.

Key words: Curly Leaf 2, CUL2, seryl-tRNA synthetase, leaf development, leaf rolling, rice