High-level expression of a novel chromoplast phosphate transporter ClPHT4;2 is required for flesh color development in watermelon

New Phytol. 2017 Feb;213(3):1208-1221. doi: 10.1111/nph.14257. Epub 2016 Oct 27.


Chromoplast development plays a crucial role in controlling carotenoid content in watermelon flesh. Modern cultivated watermelons with colorful flesh are believed to originate from pale-colored and no-sweet progenitors. But the molecular basis of flesh color formation and regulation is poorly understood. More chromoplasts and released carotenoid globules were observed in the red-fleshed fruit of the 97103 cultivar than in the pale-colored fruits of the PI296341-FR line. Transcriptome profiles of these two materials identified Cla017962, predicted as ClPHT4;2, was dramatically up-regulated during flesh color formation. High ClPHT4;2 expression levels were closely correlated with increased flesh carotenoid contents among 198 representative watermelon accessions. Down-regulation of ClPHT4;2 expression in transgenic watermelons reduced the fruit carotenoid accumulation. ClPHT4;2 as a function of chromoplast-localized phosophate transporter was tested by heterologous expression into a yeast phosphate-uptake-defective mutant, western blotting, subcellular localization, and immunogold electron microscopy analysis. Two transcription factors, ClbZIP1 and ClbZIP2, were identified, which responded to ABA and sugar signaling to regulate ClPHT4;2 transcription only in cultivated watermelon species. Our findings suggest that elevated ClPHT4;2 gene expression is necessary for carotenoid accumulation, and may help to characterize the co-development of flesh color and sweetness during watermelon development and domestication.

Keywords: Citrullus lanatus; chromoplast; flesh color; phosphate transporter; transcriptional regulation.

MeSH terms

  • Abscisic Acid / pharmacology
  • Carotenoids / biosynthesis
  • Citrullus / drug effects
  • Citrullus / genetics*
  • Citrullus / ultrastructure
  • Ecotype
  • Fruit / genetics
  • Gene Expression Regulation, Plant* / drug effects
  • Genes, Plant
  • Genetic Complementation Test
  • Glucose / pharmacology
  • Glycine / analogs & derivatives
  • Glycine / pharmacology
  • Mutation / genetics
  • Organophosphorus Compounds / pharmacology
  • Phenotype
  • Phosphate Transport Proteins / genetics*
  • Phosphate Transport Proteins / metabolism
  • Pigmentation* / drug effects
  • Plant Proteins / genetics*
  • Plant Proteins / metabolism
  • Plants, Genetically Modified
  • Plastids / drug effects
  • Plastids / metabolism*
  • Plastids / ultrastructure
  • Promoter Regions, Genetic / genetics
  • Protein Binding
  • Pyridones / pharmacology
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Response Elements / genetics
  • Subcellular Fractions / metabolism
  • Sucrose / pharmacology
  • Transcription Factors / metabolism
  • Transcription, Genetic / drug effects


  • Organophosphorus Compounds
  • Phosphate Transport Proteins
  • Plant Proteins
  • Pyridones
  • RNA, Messenger
  • Transcription Factors
  • Carotenoids
  • fluridone
  • Sucrose
  • Abscisic Acid
  • Glucose
  • aminoethoxyvinylglycine
  • Glycine
  • ethephon