## 5 Conclusions  
This is the first work to report the physiological and molecular characterization of carotenoid accumulation in R-HJH. The red pigmentation of the pummelo mutant R-HJH is due to the accumulation of lycopene, followed by \(\beta\)-carotene and _photoene_, whereas these pigments were low or undetectable in wild-type HJH pummelo. Furthermore, our study provides a global overview of the transcriptomic profile of R-HJH. The increases in the expression of upstream synthesis genes (PSY) and the decreases in the expression of downstream genes (CHYB and CCD7) might be the key aspects that account for the lycopene accumulation in R-HJH. However, additional studies are required to confirm these findings.  
**Supplementary Materials:** The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/molecules27144595/s1](https://www.mdpi.com/article/10.3390/molecules27144595/s1)]([https://www.mdpi.com/article/10.3390/molecules27144595/s1](https://www.mdpi.com/article/10.3390/molecules27144595/s1)), Figure S1. GC/MS total ion chromatograms of two different tissues of R-HJH and wild-type HJH fruits. A, flavedo of HJH; B, albedo of HJH; C, flavedo of R-HJH; and D, albedo of R-HJH. Figure S2. Volcano map of differentially expressed genes. Each point in the figure represents a gene, and the red and green dots indicate that the expression level of DEGs is upregulated and downregulated, respectively. The blue dot indicates that these genes are not significantly different. Table S1: quality analysis of transcriptome sequencing data; Table S2: differentially expressed genes (DEGs) in R-HJH compared with wild-type HJH; Table S3: GO functional classification of differentially expressed genes (DEGs) in R-HJH compared with wild-type HJH; Table S4: KEGG enrichment analysis of differentially expressed genes (DEGs) in R-HJH compared with wild-type HJH; Table S5: DEGs involved in carotenoid accumulation.  
**Author Contributions:** [PERSON] carried out the research, analyzed the data, wrote and revised the manuscript; [PERSON] carried out UPLC analysis; [PERSON] carried out HS-SPME and GC-MS analysis; [PERSON] provided material, designed the experiments, and gave important suggestions. All authors have read and agreed to the published version of the manuscript.  
**Funding:** The APC was funded by Agricultural Competitive Industry Discipline Team Building Project of Guangdong Academy of Agricultural Sciences (202113 TD).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Acknowledgments:** The authors gratefully acknowledge the financial support from National Key Research and Development Program of China (No. 2020 YFD1001101), Guangdong Province Science and Technology Plan Project (No. 2018B020202009), the National Modern Agricultural (Citrus) Technology Systems of China (No. CARS-26), Natural Science Foundation of Guangdong Province (No. 2020A1515010167), Agricultural Competitive Industry Discipline Team Building Project of Guangdong Academy of Agricultural Sciences (No. 20213 TD), Special Fund for Scientific Innovation Strategy-Construction of High Level Academy of Agriculture Science (No. R2020 PY-JGO01) and Independent Research and Development Projects of Maoming Laboratory (No. 2021 ZZ004).  
**Conflicts of Interest:** The authors declare that they have no conflict of interest.  
**Sample Availability:** Samples of R-HJH and wild-type HJH are available from the authors.