*Article LEAF TIP RUMPLED 1* **Regulates Leaf Morphology and Salt Tolerance in Rice**

**Jiajia Wang 1,2,†, Yiting Liu 1,3,†, Songping Hu <sup>3</sup> , Jing Xu <sup>1</sup> , Jinqiang Nian <sup>1</sup> , Xiaoping Cao <sup>1</sup> , Minmin Chen <sup>1</sup> , Jiangsu Cen <sup>1</sup> , Xiong Liu <sup>1</sup> , Zhihai Zhang <sup>1</sup> , Dan Liu <sup>3</sup> , Li Zhu <sup>1</sup> , Jiang Hu <sup>1</sup> , Deyong Ren <sup>1</sup> , Zhenyu Gao <sup>1</sup> , Lan Shen <sup>1</sup> , Guojun Dong <sup>1</sup> , Qiang Zhang <sup>1</sup> , Qing Li <sup>1</sup> , Sibin Yu <sup>2</sup> , Qian Qian 1,\* and Guangheng Zhang 1,4,\***


**Abstract:** Leaf morphology is one of the important traits related to ideal plant architecture and is an important factor determining rice stress resistance, which directly affects yield. Wax layers form a barrier to protect plants from different environmental stresses. However, the regulatory effect of wax synthesis genes on leaf morphology and salt tolerance is not well-understood. In this study, we identified a rice mutant, *leaf tip rumpled 1* (*ltr1*), in a mutant library of the classic *japonica* variety Nipponbare. Phenotypic investigation of NPB and *ltr1* suggested that *ltr1* showed rumpled leaf with uneven distribution of bulliform cells and sclerenchyma cells, and disordered vascular bundles. A decrease in seed-setting rate in *ltr1* led to decreased per-plant grain yield. Moreover, *ltr1* was sensitive to salt stress, and *LTR1* was strongly induced by salt stress. Map-based cloning of *LTR1* showed that there was a 2-bp deletion in the eighth exon of *LOC\_Os02g40784* in *ltr1*, resulting in a frameshift mutation and early termination of transcription. Subsequently, the candidate gene was confirmed using complementation, overexpression, and knockout analysis of *LOC\_Os02g40784*. Functional analysis of *LTR1* showed that it was a wax synthesis gene and constitutively expressed in entire tissues with higher relative expression level in leaves and panicles. Moreover, overexpression of *LTR1* enhanced yield in rice and *LTR1* positively regulates salt stress by affecting water and ion homeostasis. These results lay a theoretical foundation for exploring the molecular mechanism of leaf morphogenesis and stress response, providing a new potential strategy for stress-tolerance breeding.

**Keywords:** *Oryza sativa* L.; leaf shape; salt stress; bulliform cells; aquaporin
