The color and pattern of watermelon rind are crucial external traits that directly affect consumer preferences.  Watermelons with stripes having a stronger color than the background rind are ideal for studying stripe patterns in plants, while there is still limited knowledge about the genetic mechanisms underlying stripe coloration due to the lack of germplasm resources.  In this study, we focused on a watermelon germplasm with colorless stripes, and genetic analysis revealed that the trait is controlled by a single recessive gene.  The gene Clsc (Citrullus lanatus stripe coloration), which is responsible for the colorless stripe, was localized into a 147.6 kb region on Chr9 by linkage analysis in a large F₂ mapping population.  Further analysis revealed that the Cla97C09G175170 gene encodes the APRR2 transcription factor, plays a crucial role in determining the watermelon colorless stripe phenotype and was deduced to be related to chlorophyll synthesis and chloroplast development.  Physiological experiments indicated that Cla97C09G175170 may significantly influence chloroplast development and chlorophyll synthesis in watermelon.  The results of this study provide a better understanding of the molecular mechanism of stripe coloration in watermelon and can be useful in the development of marker-assisted selection (MAS) for new watermelon cultivars.

Watermelon (Citrullus lanatus) holds global significance as a fruit with high economic and nutritional value.  Exploring the regulatory network of watermelon male reproductive development is crucial for developing male sterile materials and facilitating cross-breeding.  Despite its importance, there is a lack of research on the regulation mechanism of male reproductive development in watermelon.  In this study, we identified that ClESR2, a VIIIb subclass member in the APETALA2/Ethylene Responsive Factor (AP2/ERF) superfamily, was a key factor in pollen development.  RNA in situ hybridization confirmed significant ClESR2 expression in the tapetum and pollen during the later stage of anther development.  The pollens of transgenic plants showed major defects in morphology and vitality at the late development stage.  The RNA-seq and protein interaction assay confirmed that ClESR2 regulates pollen morphology and fertility by interacting with key genes involved in pollen development at both transcriptional and protein levels.  These suggest that Enhancer of Shoot Regeneration 2 (ESR2) plays an important role in pollen maturation and vitality.  This study helps understand the male reproductive development of watermelon, providing a theoretical foundation for developing male sterile materials.