类胡萝卜素是西瓜果肉颜色和营养品质形成的重要物质基础，而有色体是西瓜果肉中类胡萝卜素合成与积累的关键场所。申请人前期对西瓜果肉颜色性状进行了全基因组关联分析，经比较转录组学和序列比对分析后，确定Orange（Or）基因是参与调控西瓜果肉有色体分化及类胡萝卜素积累的重要基因，但其具体的调控机制尚不清楚。本项目拟通过基因表达、亚细胞定位、遗传转化和构建Or基因的近等基因系等技术，明确Or基因在果肉中调节有色体分化与类胡萝卜素积累的重要基因功能，同时利用酵母杂交、转录组测序和染色质免疫沉淀测序等技术，解析Or基因在果肉有色体分化和类胡萝卜素积累中的分子作用机制及其调控网络。研究结果将进一步丰富和完善Or基因调节有色体分化与类胡萝卜素积累的分子机制，也将为西瓜的果实品质改良提供理论基础和可靠依据。

Carotenoids are an important material basis for the formation of flesh color and nutritional quality in Citrullus lanatus, chromoplast is the key organelle for the synthesis and accumulation of carotenoids in watermelon flesh. We conducted a genome-wide association study (GWAS) on the flesh color traits of watermelon. Orange (Or) gene was confirmed a candidate gene to regulate the chromoplast differentiation and carotenoid accumulation in watermelon flesh after comparative transcriptomics and sequence alignment analysis. However, the molecular mechanism of Or gene is still not clear and remains elusive. In this project, we will explore the function of Or gene in regulating chromoplast differentiation and carotenoid accumulation by gene expression analysis, subcellular localization, genetic transformation and construction of near iso-genic lines (NIL). Meanwhile, we will combine yeast hybridization, transcriptome sequencing (RNA-seq) and chromatin immunoprecipitation sequencing (ChIP-Seq) to reveal the molecular mechanism and its regulatory network of Or gene in regulating the chromoplast differentiation and carotenoids accumulation. The results will not only enrich the molecular mechanism of Or gene in regulating chromoplast differentiation and carotenoid accumulation, but also provide a theoretical basis for the genetic improvement of fruit quality in watermelon.