Volatile content and genetic variation of citron in Tibet and Yunnan

Citron (Citrus medica) is a representative aromatic species of the Citrus genus in the Rutaceae family. To determine the volatile profiles and genetic variation of citron, we collected 218 citron accessions within China, including 130 from Yunnan and 88 from Tibet. We identified a total of 80 volatile compounds from their pericarps. Among the volatile profiles, monoterpenes were identified as the predominant compounds, with d-limonene being the most abundant. The correlation analysis indicated that the content of 5 volatile compounds was significantly associated with the proportion of juice vesicles in citron fruits. Citrons from Tibet exhibited a higher total volatile content and lower variability in their volatile profile than those from Yunnan. Comparative analysis revealed significant differences in the levels of 48 volatile compounds between Tibetan and Yunnan citrons. Furthermore, we assembled a 402.23-Mb chromosome-scale citron genome (contig N50 = 37.51 Mb) and resequenced 105 representative citron accessions. The population structure analysis divided these citron accessions into two populations: Yunnan and Tibet. The nucleotide diversity in the Tibet population was significantly lower than that in the Yunnan population on a genome-wide scale. Based on d-limonene content, we identified JUNGBRUNNEN1-like (CmJUB1-like), a NAC transcription factor, (-) on chromosome 7 through a genome-wide association study. Overexpressing CmJUB1-like significantly enhanced d-limonene and total monoterpene levels in citron. These results broaden our understanding of the genetic mechanisms influencing volatile profiles and may facilitate the molecular breeding of citrus.