Comparative Analyses of Chloroplast Genomes of Cucurbitaceae Species: Lights into Selective Pressures and Phylogenetic Relationships

Cucurbitaceae is the fourth most important economic plant family with creeping herbaceous species mainly distributed in tropical and subtropical regions. Here, we described and compared the complete chloroplast genome sequences of ten representative species from Cucurbitaceae. The lengths of the ten complete chloroplast genomes ranged from 155,293 bp (C. sativus) to 158,844 bp (M. charantia), and they shared the most common genomic features. 618 repeats of three categories and 813 microsatellites were found. Sequence divergence analysis showed that the coding and IR regions were highly conserved. Three protein-coding genes (accD, clpP, and matK) were under selection and their coding proteins often have functions in chloroplast protein synthesis, gene transcription, energy transformation, and plant development. An unconventional translation initiation codon of psbL gene was found and provided evidence for RNA editing. Applying BI and ML methods, phylogenetic analysis strongly supported the position of Gomphogyne, Hemsleya, and Gynostemma as the relatively original lineage in Cucurbitaceae. This study suggested that the complete chloroplast genome sequences were useful for phylogenetic studies. It would also determine potential molecular markers and candidate DNA barcodes for coming studies and enrich the valuable complete chloroplast genome resources of Cucurbitaceae.