Chilling stress (CS) is an important limiting factor for the growth and development of passion fruit (Passiflora edulis) in winter in South China. However, little is known about how the passion fruit responds and adapts to CS. In this study, we performed transcriptome sequencing of cold-susceptible cultivar Huangjinguo (HJG) and cold-tolerant cultivar Tainong 1 (TN1) under normal temperature (NT) and CS conditions, and a total of 47,353 unigenes were obtained by seven databases. Using differentially expressed unigenes (DEGs) analysis, 3,248 and 4,340 DEGs were identified at two stages, respectively. The Gene Ontology (GO) enrichment analysis showed that the DEGs were mainly related to phosphorylation, membrane protein, and catalytic activity. In Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway, the unigenes of plant-pathogen interaction, plant hormone signal transduction and fatty acid metabolism were enriched. Then, the 12,471 filtered unigenes were clustered into eight co-expression modules, and two modules were correlated with CS. In this two modules, 32 hub unigenes were obtained. Furthermore, the unigenes related to CS were validated using quantitative real-time PCR (RT-qPCR). This work showed that the expression levels of CS-related unigenes were very different in two passion fruit cultivars. The results provide information for the development of passion fruit with increased chilling tolerance.

Background: The passion fruit (Passiflora edulis Sims) is a diploid plant (2n = 2x = 18) and is a perennial scrambling vine in Southern China. However, the occurrence and spread of stem rot in passion fruit severely impact its yield and quality. Methods: In this study, we re-sequenced a BC1F1 population consisting of 158 individuals using whole-genome resequencing. We constructed a high-density genetic linkage map and identified the quantitative trait locus (QTL), and analyzed candidate genes associated with stem rot resistance in passion fruit. Results: Based on the passion fruit reference genome (MER), a high-density genetic linkage map was constructed with 1,180,406 single nucleotide polymorphisms (SNPs). The map contains nine linkage groups, covering a total genetic distance of 1559.03 cM, with an average genetic distance of 311.81 cM. The average genetic distance between 4206 bins was 0.404 cM, and the average gap length was 10.565 cM. The collinearity correlation coefficient between the genetic map and the passion fruit genome was 0.9994. Fusarium solani was used to infect the BC1F1 population, and the resistance to stem rot showed a continuous distribution. A QTL, qPSR5, was mapped to the 113,377,860 bp–114,811,870 bp genomic region on chromosome 5. We performed RNA sequencing (RNA-seq) and real-time quantitative polymerase chain reaction (RT-qPCR) to analyze the expression levels of predicted genes in the candidate region and identified ZX.05G0020740 and ZX.05G0020810 as ideal candidate genes for stem rot resistance in passion fruit. Conclusions: The findings in this study not only lay the foundation for cloning the qPSR5 responsible for stem rot resistance but also provide genetic resources for the genetic improvement of passion fruit.

Stem rot disease poses a significant challenge in passion fruit production, necessitating the identification of resistant genes for the development of stem rot resistant varieties. In this study, we conducted artificial inoculation of Fusarium solani on leaves of two passion fruit varieties, 'Huangjinguo' and 'Ziguo 7'. Leaf samples were collected at 0 h, 24 h, and 48 h post-inoculation for RNA-sequencing (RNA-seq) analysis, and 3 370, 4 464, and 3 974 differentially expressed genes (DEGs) were identified at these stages. Gene Ontology (GO) analysis revealed associations with functions such as response to reactive oxygen species (ROS), response to hydrogen peroxide, and protein complex oligomerisation. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis highlighted the enrichment of DEGs in the phenylpropanoid biosynthesis pathway, including genes such as ZX.06G0025070, ZX.01G0064640, ZX.04G0011040, ZX.05G0011380, all implicated in lignin biosynthesis. Weighted gene co-expression network analysis (WGCNA) identified three modules significantly associated with passion fruit stem rot resistance. Network analysis highlighted ZX.08G0013660 as the gene with the highest connectivity in these modules, featuring a leucine-rich repeat domain. Reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) analysis further validated ZX.08G0013660 and other genes as potential candidates for passion fruit stem rot resistance. Overall, genes related to ROS, phenylpropanoid biosynthesis and leucine-rich repeat domain protein likely play critical roles in passion fruit stem rot resistance. This study provides new insights for breeding passion fruit varieties resistant to stem rot disease.

Information of the Passiflora genome is still very limited. Understand the evolutionary relationship between different species of Passiflora , and develop a large number of SSR markers to provide a basis for the genetic improvement of Passiflora . Applying restriction site associated DNA sequencing (RAD-Seq) technology, we studied the phylogeny, simple sequence repeat (SSR) and marker transferability of 10 accessions of 6 species of Passiflora . Taking the partial assembly sequence of accessions P4 as the reference genome, we constructed the phylogenetic tree using the detected 46,451 high-quality single nucleotide polymorphisms (SNPs), showing that P6, P7, P8 and P9 were a single one while P5 and P10 were clustered together, and P1, P2, P3 and P4 were closer in genetic relationship. Using P8 as the reference genome, a total of 12,452 high-quality SNPs were used to construct phylogenetic tree. P3, P4, P7, P8, P9 and P10 were all single branch while P1 and P2 were clustered together, and P5 and P6 were clustered into one branch. A principal component analysis (PCA) revealed a similar population structure, which four cultivated passion fruits forming a tight cluster. A total of 2,614 SSRs were identified in the genome of 10 Passiflora accessions. The core motifs were AT, GA, AAG etc., 2-6 bases, 4-16 repeats, and 2,515 pairs of SSR primer were successfully developed. T the SSR transferability in cultivated passion fruits is the best. These results will contribute to the study of genomics and molecular genetics in passion fruit.

The cultivated passion fruit (Passiflora edulis) is a diploid plant (2n=2x=18) and is an important fruit tree in southern China. However, the occurrence and spread of stem rot in passion fruit severely impact its yield and quality. This study aims to construct a high-density genetic linkage map and identify the quantitative trait locus (QTL) and candidate genes associated with stem rot resistance in passion fruit. In this study, we used an HG and ZG7 hybrid to develop a BC1F1 population consisting of 158 individuals. Take a previously published passion fruit genome as reference, a high-density genetic linkage map was constructed with 1,180,406 single nucleotide polymorphisms (SNPs). The map contains 9 linkage groups, covering a total genetic distance of 1559.03 cM, with an average genetic distance of 311.81 cM. The average genetic distance between 4206 bins was 0.404 cM, and the average gap length was 10.565 cM. The collinearity correlation coefficient between the genetic map and the passion fruit genome was 0.9994. Fusarium solani was used to infect the BC1F1 population, and the resistance to stem rot showed a continuous distribution. A QTL, qPSR5, was identified in the 145.878-152.951 cM region on the 5th linkage group. We performed RNA-seq and RT-qPCR to analyze the expression levels of predicted genes in the candidate region and identified ZX.05G0020740 and ZX.05G0020810 as ideal candidate genes for stem rot resistance in passion fruit. The findings in this study not only lay the foundation for cloning the qPSR5 responsible for stem rot resistance but also provide genetic resources for the genetic improvement of passion fruit.