Background The TIFY gene family is a group of plant-specific transcription factors involved in regulation of plant growth and development and a variety of stress responses. However, the TIFY family has not yet been well characterized in kiwifruit, a popular fruit with important nutritional and economic value. Results A total of 27 and 21 TIFY genes were identified in the genomes of Actinidia eriantha and A. chinensis, respectively. Phylogenetic analyses showed that kiwifruit TIFY genes could be classified into four major groups, JAZ, ZML, TIFY and PPD, and the JAZ group could be further clustered into six subgroups (JAZ I to JAZ VI). Members within the same group or subgroup have similar exon-intron structures and conserved motif compositions. The kiwifruit TIFY genes are unevenly distributed on the chromosomes, and the segmental duplication events played a vital role in the expansion of the TIFY genes in kiwifruit. Syntenic analyses of TIFY genes between kiwifruit and other five plant species (including Arabidopsis thaliana, Camellia sinensis, Oryza sativa, Solanum lycopersicum and Vitis vinifera) and between the two kiwifruit species provided valuable clues for understanding the potential evolution of the kiwifruit TIFY family. Molecular evolutionary analysis showed that the evolution of kiwifruit TIFY genes was primarily constrained by intense purifying selection. Promoter cis-element analysis showed that most kiwifruit TIFY genes possess multiple cis-elements related to stress-response, phytohormone signal transduction and plant growth and development. The expression pattern analyses indicated that TIFY genes might play a role in different kiwifruit tissues, including fruit at specific development stages. In addition, several TIFY genes with high expression levels during Psa (Pseudomonas syringae pv. actinidiae) infection were identified, suggesting a role in the process of Pas infection. Conclusions In this study, the kiwifruit TIFY genes were identified from two assembled kiwifruit genomes. In addition, their basic physiochemical properties, chromosomal localization, phylogeny, gene structures and conserved motifs, synteny analyses, promoter cis-elements and expression patters were systematically examined. The results laid a foundation for further understanding the function of TIFY genes in kiwifruit, and provided a new potential approach for the prevention and treatment of Psa infection.

Actinidia eriantha is a unique germplasm resource for kiwifruit breeding. Genetic diversity and nutrient content need to be evaluated prior to breeding. In this study, we looked at the metabolites of three elite A. eriantha varieties (MM-11, MM-13 and MM-16) selected from natural individuals by using a UPLC-MS/MS-based metabolomics approach and transcriptome, with a total of 417 metabolites identified. The biosynthesis and metabolism of phenolic acid, flavonoids, sugars, organic acid and AsA in A. eriantha fruit were further analyzed. The phenolic compounds accounted for 32.37% of the total metabolites, including 48 phenolic acids, 60 flavonoids, 7 tannins and 20 lignans and coumarins. Correlation analysis of metabolites and transcripts showed PAL (DTZ79_15g06470), 4CL (DTZ79_26g05660 and DTZ79_29g0271), CAD (DTZ79_06g11810), COMT (DTZ79_14g02670) and FLS (DTZ79_23g14660) correlated with polyphenols. There are twenty-three metabolites belonging to sugars, the majority being sucrose, glucose arabinose and melibiose. The starch biosynthesis-related genes (AeglgC, AeglgA and AeGEB1) were expressed at lower levels compared with metabolism-related genes (AeamyA and AeamyB) in three mature fruits of three varieties, indicating that starch was converted to soluble sugar during fruit maturation, and the expression level of SUS (DTZ79_23g00730) and TPS (DTZ79_18g05470) was correlated with trehalose 6-phosphate. The main organic acids in A. eriantha fruit are citric acid, quinic acid, succinic acid and D-xylonic acid. Correlation analysis of metabolites and transcripts showed ACO (DTZ79_17g07470) was highly correlated with citric acid, CS (DTZ79_17g00890) with oxaloacetic acid, and MDH1 (DTZ79_23g14440) with malic acid. Based on the gene expression, the metabolism of AsA acid was primarily through the L-galactose pathway, and the expression level of GMP (DTZ79_24g08440) and MDHAR (DTZ79_27g01630) highly correlated with L-Ascorbic acid. Our study provides additional evidence for the correlation between the genes and metabolites involved in phenolic acid, flavonoids, sugars, organic acid and AsA synthesis and will help to accelerate the kiwifruit molecular breeding approaches.

In order to better understand the changes in fruit quality and soluble sugar components in wild Actinidia eriantha at the soft ripening stage, this study explored the fruit quality indexes, soluble sugar components, sucrose metabolism-related enzyme activities and the expression of sucrose metabolism-related enzyme genes in wild A. eriantha germplasm resources. The results showed that the fruit quality of wild A. eriantha at the soft ripening stage was quite different, and the coefficient of variation of fructose content was the largest, followed by sucrose and glucose. Principal component analysis and systematic clustering analysis showed that the comprehensive performance of fruit quality indexes of M28 and M10 was the most prominent. The accumulation and composition of soluble sugar components in different wild A. eriantha varieties (lines) were not consistent. The activities of sucrose metabolism enzymes among wild A. eriantha varieties (lines) were different to some extent. The sucrose metabolism-related enzyme genes among wild A. eriantha germplasm resources had different expression patterns. The results will contribute to understanding the fruit quality changes and the mechanism of sugar metabolism in wild A. eriantha at the soft ripening stage, and lay a foundation for the protection and utilization of wild A. eriantha germplasm resources.