Primary Bitter Taste of Citrus is Linked to a Functional Allele of the 1,2-Rhamnosyltransferase Gene Originating from Citrus grandis

1,2-Rhamnosyltransferase (1,2RhaT) catalyzes the final step of production of flavanone neohesperidoside (FNH) that is responsible for the primary bitter taste of citrus fruits. In this study, species-specific flavonoid profiles were determined in 87 Citrus accessions by identifying eight main flavanone glycosides (FGs). Accumulation of FNHs was completely correlated to the presence of the 1,2RhaT gene in 87 citrus accessions analyzed using a novel 1,2RhaT-specific DNA marker. Pummelo (Citrus grandis) was identified as the genetic origin for a function allele of 1,2RhaT that underpinned FNH-bitterness in modern citrus cultivars. In addition, genes encoding six MYB and five bHLH transcription factors were shown to coexpress with 1,2RhaT and other flavonoid pathway genes related to FNH accumulation, indicating that these transcription factors may affect the fruit taste of citrus. This study provides a better understanding of bitterness formation in Citrus varieties and a genetic marker for the early selection of nonbitterness lines in citrus breeding programs.