Genetic Mapping and Functional Characterisation of GhCUP Regulating Leaf Curling in Cotton

Leaf size and shape are crucial traits affecting photosynthesis. Moderate leaf curling is believed to be beneficial to photosynthesis because upright leaves are ideal for building a canopy structure with reduced shaded areas to improve light penetration and ventilation. In this study, we investigated the cytological features of a natural cotton mutant showing cup-shaped leaves due to upward curling of leaf edge and identified the gene regulating leaf edge curling. Genetic analysis indicates that the cup-shaped leaf is caused by mutations in an incomplete dominant gene, designated GhCUP. The gene was mapped to a 206-kb genomic region containing 16 annotated genes in chromosome A11. Based on the annotation and expression difference of the genes in the interval between the mutant and cotton cultivar with normal leaf shape, virus-induced gene silencing, and gene overexpression, GH_A11G3479 was identified as GhCUP. The promoter sequence of GhCUP contains several cis-elements that could potentially interact with transcription factors involved in leaf development, with some of them mutated in the cup-shaped leaf mutant. One of those mutations was in a binding site of KAN1, which might contribute to up-regulation of GhCUP in the mutant, leading to the mutant phenotype, as KAN1 could interact with the promoter of GhCUP from cotton cultivar with normal leaf shape but binding affinity to the mutant promoter was significantly reduced. Identifying GhCUP provides a novel gene for creating ideal canopy structure by manipulating cotton leaf shape.