Pitaya (Hylocereus undatus) is one of the most economic fleshy fruit tree crops. This study aimed at producing a high-density linkage genetic map of pitaya based on the whole genome resequencing (WGrS) approach. For this purpose, a bi-parental F1 population of 198 individuals was generated and genotyped by WGrS. High-quality polymorphic 6434 single polymorphism nucleotide (SNP) markers were extracted and used to construct a high-density linkage map. A total of 11 linkage groups were resolved as expected in accordance with the chromosome number. The map length was 14,128.7 cM with an average SNP interval of 2.2 cM. Homology with the sequenced reference genome was described, and the physical and genetic maps were compared with collinearity analysis. This linkage map in addition to the available genomic resources will help for quantitative trait mapping, evolutionary studies and marker-assisted selection in the important Hylocereus species.

Dragon fruit comprises a wide variety of species that are rich in nutritional value and have great economic potential; however, numerous studies have focused on their nutritional and commercial quality. In contrast, few studies have addressed their flavor quality, particularly with respect to the regulatory networks responsible for their flavor-related substance contents. To this end, we sequenced the transcriptomes and metabolomes of red-skin/white-fleshed and red-skin/red-fleshed dragon fruit at different timepoints during fruit development. RNA-seq and metabolome data were used to divide the seven developmental stages of the dragon fruit into four categories (young fruit, expansion, maturity, and senescence). In all, 16,827 differentially expressed genes (DEGs), including 958 transcription factors, were identified and grouped into 10 clusters, and the pathways in each cluster were annotated. Additionally, 318 differentially accumulated metabolites (DAMs) were identified, including 88 common metabolites. The main flavor-related substances and the key genes regulating them were determined via joint analysis via RNA-seq and metabolomics. Furthermore, 10 volatile active components related to green flavors and aromas were screened according to the relative odor activity value (ROAV), and 15 candidate genes related to key flavor compounds were screened via WGCNA, 3 of which encoded transcription factors. In conclusion, our results provide a theoretical basis for an in-depth understanding of the volatile flavor compounds in dragon fruit and provide new genetic resources for the subsequent study of fruit flavor compounds.

High temperature (HT) is one of the most adverse environmental stresses altering the quality value of fruits. However, knowledge of the molecular responses of pitaya to HT stress remains elusive. Hence, the present study aimed to reveal key HT tolerance mechanisms of pitaya through an integrated transcriptome and proteome analysis of two contrasting varieties, C-130 (heat tolerant) and H17-10 (heat sensitive). We identified a total of 5783 DEGs (differentially expressed genes) and 2101 DEPs, of which 376 DEGs and DEPs were significantly correlated. Enrichment analyses unveiled biosynthesis of secondary metabolites, plant hormone signal transduction, MAPK-signaling pathway-plant, protein processing in endoplasmic reticulum, pyruvate metabolism, and cysteine and methionine metabolism as the key molecular responsive mechanisms. Particularly, heat shock transcription factors (HSFs), glutathione metabolism and brassinosteroids (BR) are essential for heat tolerance in pitaya. Major induced genes in these pathways were filtered out and examined. Furthermore, we uncovered 18 potential candidate genes for improving pitaya heat tolerance capability. Particular attention should be paid to the genes HU05G01771 and HU10G01257 encoding cytochrome P450 85A-like (related to BR synthesis) and HSF B-2a, respectively. Our findings disclose key molecular players responding to HT in pitaya, providing genetic resources for enhancing the crop heat tolerance.