Comparative transcriptome analysis and heterologous overexpression indicate that the ZjZOG gene may positively regulate the size of jujube fruit

Abstract

Background: Fruit size is a crucial economic trait that impacts the quality of jujube (Ziziphus jujuba), however, research in this area remains limited. This study utilized two jujube cultivars with similar genetic backgrounds but differing fruit sizes to investigate the regulatory mechanisms affecting fruit size through cytological observations, transcriptome sequencing, and heterologous overexpression.

Results: The findings reveal that variations in mesocarp cell numbers during early fruit development significantly influence final fruit size. Comparative transcriptome sequencing identified 16,778 differentially expressed genes across five developmental stages. Co-expression network analysis identified 16 co-expression modules. KEGG enrichment analysis of these modules indicated the significant role of plant hormone-related pathways in fruit development. A detailed analysis of the 'sky blue' module revealed candidate genes associated with the regulation of mesocarp cells, leading to the construction of a regulatory network. Heterologous overexpression of the candidate gene ZjZOG in tomato confirmed its positive role in fruit size enhancement. Transcriptomic analysis of these overexpression lines further validated the regulatory network and identified reliable candidate genes for fruit size control.

Conclusion: This study provides valuable insights into the regulatory mechanisms of fruit size, which may facilitate the breeding of larger jujube cultivars.

Keywords: Ziziphus jujuba; ZjZOG; Fruit size; Transcriptomics.

Fig. 1

Development of the fruit of ‘LH’ and ‘ZY’. (A) Fruit weight. (B) Fruit weight in fruit set and mature stage. (C) The cell numbers of mesocarp. (D) The cell numbers of mesocarp fruit weight in fruit set and mature stage. (E) The cell length of mesocarp. (F) The cell length of mesocarp fruit weight in fruit set and mature stage. The asterisks represent significant differences determined by the student’s t-test at P < 0.05

Fig. 2

(A) The number of DEGs at each stage. (B) Venn diagrams showing overlaps of expressed genes in the samples of the five stages

Fig. 3

(A) Network analysis dendrogram showing modules identified by WGCNA (weighted gene co-expression network analysis): dendrogram with color annotation. (B) Heat map of the expression of the top ten genes in the ‘sky blue’ module. (C) Subnetwork of the top ten genes in the ‘sky blue’ module

Fig. 4

Phenotype observation of overexpression lines. (A) Tomato fruit morphology of wild-type and three ZjZOG overexpression lines. (B) Transcript levels of ZjZOG in the wild-type (WT) tomato and three overexpression transgenic lines. (C-E) Statistical data of tomato fruit weight, width, and length in wild-type and three ZjZOG overexpression lines. ‘**’ indicated P < 0.01

Fig. 5

(A) Volcano map of DEGs. (B) Venn diagrams showing overlaps of DEGs in three ZjZOG-OE lines

Fig. 6

(A) Representation of the 25 most-enriched GO terms. (B) Representation of the 25 most-enriched KEGG pathways. The significance of the enrichment factor is indicated by the coloring of the q-values

Fig. 7

Expression heat map of 16 cyclin or cyclin-dependent kinase-related genes in overexpression lines and wild type

Fig. 8

Potential mode of action of ZjZOG Gene in regulating jujube fruit size