Fine Mapping Identifies ClTFL1 Encodes a TERMINAL FLOWER 1 Protein as Putative Candidate Gene for Inflorescence Architecture and Tendril Development and in Watermelon

Tendrils are threadlike organs in vining plants that play essential role in climbing to reach more sunlight and growing space. However, the molecular basis underlying tendril organogenesis has only been studied in a few taxa. Here, a tendril-less watermelon mutant CG149 with determinate inflorescence was identified. Genetic analysis showed that the two traits of tendril-less and determinate inflorescence were co-segregated and were controlled by a single recessive gene, termed as Cltl/df . Bulked segregant sequencing and map-based cloning delimited the Cltl/df locus into a 61.6 kb region in watermelon chromosome 4. Gene sequence and expression analysis revealed that gene Cla97C04G076830 ( ClTFL1 ) encodes a TERMINAL FLOWER 1 protein as the most probable candidate gene for Cltl/df . A single nucleotide mutation from C to A in the fourth exon was identified in ClTFL1 , which resulted in a mutation from alanine to glutamic acid within a conserved motif of the TFL1 protein. Further qRT-PCR analysis showed that the expression level of ClTFL1 was significantly down-regulated in the inflorescence of the tendril-less mutant. The results of this study reveal the pleiotropic effects of ClTFL1 in regulating watermelon architecture and provide molecular mechanism of tendril organogenesis in angiosperms.