In this study, transcriptome analyses were carried out on the fruits of Kurakato Wase peach and its early-ripening mutant at different developmental stages. The key factors involved in fruit ripening regulation were explored, so as to provide a theoretical basis for further study on the regulation mechanism of fruit ripening.

The flesh of Kurakato Wase peach and its early-ripening mutant was sampled at 30 d, 45 d, 59 d, 71 d, and 89 d after anthesis, and transcriptome analyses were performed on the above samples. The candidate differentially expressed genes (DEGs) were verified by quantitative real-time PCR (qRT-PCR). The biological function of DEGs were analyzed through GO function and KEGG pathway. The weighted gene co-expression network analysis (WGCNA) was constructed to identify the hub modules and hub genes closely related to fruit ripening.

Four comparison groups including y1 vs c1, y2 vs c2, y3 vs c4 and y4 vs c5 were obtained based on fruit development stages. A tatal of 4 395 DEGs were identified with 2 212 up- and 2 183 down-regulated genes. There were 10, 11 and 18 candidate genes involved in ethylene, abscisic acid and auxin synthesis and signal transduction, respectively. The interaction networks between 10 IAA proteins and their predictive interacting proteins ARF were constructed. GO function revealed that the DEGs were mainly enriched in cellular processes, metabolic processes and monomeric processes in the biological process category; in cell component category, DEGs were mainly enriched in membranes and cellular components; in molecular function category, DEGs were mainly enriched in binding protein and catalytic activity. There were more DEGs in comparison groups y3 vs c4 and y4 vs c5, and these DEGs mainly enriched in molecular functions, such as binding and catalytic activity. The KEGG pathway analysis showed that a variety of secondary metabolites changed during fruit development and ripening, such as sesquiterpene and triterpenoid biosynthesis, flavonoid biosynthesis, carotenoid biosynthesis, and α-linolenic acid metabolism. In addition, auxin signal transduction pathway was found to be enriched at different time nodes.

Among DEGs, a large number of hormone signal transduction pathway genes, especially auxin signal pathway genes, were enriched, and these genes might play an extremely important role during fruit ripening. The functions of candidate genes IAA and ARF and the molecular regulation of fruit ripening would be further elucidated in the future studies.

The object of this study was to isolate a peach potential-related gene PpSAUR73, to analyze its expression response to hormones, and to identify its role in regulating seedling growth in transgenic Arabidopsis, so as to provide the molecular basis for the regulation of tree potential.

Using Zhongyou Pan 9 as the material for hormone treatment, the real-time fluorescence quantitative analysis was used to analyze the dynamic response of PpSAUR73 within 24 hours. PpSAUR73 was cloned from the peach variety Jiuyan. PpSAUR73 overexpression vector was constructed and transformed into Arabidopsis. Phenotypic observation of genetical modified Arabidopsis was carried out, and the germination rate statistics of both genetically modified and wild-type Arabidopsis sown simultaneously were performed too. The root length and hypocotyl of 7-day growing Arabidopsis with consistent germination were measured, and Arabidopsis with consistent germination was treated with different concentration hormone. Transcriptome sequencing was performed using 7-day-old seedlings, and the differentially expressed genes were analyzed by functional analysis, KEGG pathway enrichment analysis, and regulatory genes analysis, respectively.

PpSAUR73 could respond quickly to hormone treatments. The overexpression of PpSAUR73 could affect the germination of Arabidopsis seeds. The hypocotyl and root length of seedlings were longer than those of wild type. In addition, the rosette of transgenic Arabidopsis was larger, and the overall growth potential was larger than wild type. The transgenic Arabidopsis showed decreased sensitivity to auxin. The transcriptome analysis of overexpressing PpSAUR73 showed that there were 128 differentially expressed genes in both control groups, including 84 up-regulated genes and 44 down-regulated genes, and 20 differentially expressed genes were described. The GO function significant enrichment analysis of the differentially expressed genes generated by overexpression of PpSAUR73 showed that the differentially expressed genes were the most abundant in cell components, located in cytoplasm, cell membrane, organelle and extracellular regions. KEGG pathway enrichment analysis on differentially expressed genes were conducted, and the results showed that the differentially expressed genes in pairwise comparisons CK vs SAUR73-1 and CK vs SAUR73-14 were mainly enriched in phenylalanine biosynthesis pathway, plant hormone signal transduction pathway, starch sucrose metabolic pathway and other metabolic pathways. In the phenylalanine biosynthesis pathway, PpSAUR73 could regulate the upregulation of peroxidase encoding genes AT1G05260, AT3G01190, AT3G32980 and AT5G15180. Peroxidases were associated with lignin synthesis, and lignin content was significantly correlated with plant growth, suggesting that overexpression of PpSAUR73 might be involved in regulating lignin synthesis in Arabidopsis and thus growth. In plant hormone signal transduction pathway, the expression of some auxin responsive genes of AtSAUR41, AtSAUR71, AtSAUR51, AtSAUR72 and AtSAUR1 in auxin signal transduction pathway was down-regulated, the expression of phosphatase protein AtPP2CA in abscisic acid signal transduction pathway was up-regulated, and the expression of abscisic acid signal pathway gene AtPYL5 was down-regulated. PpSAUR73 could regulate the growth of Arabidopsis and participate in multiple hormone signal transduction pathways.

This study found that PpSAUR73 could quickly respond to hormones and regulate the growth in transgenic Arabidopsis. The differentially expressed genes caused by overexpressed genes caused by overexpression of PpSAUR73 were mainly enriched in metabolic pathways, such as phenylalanine biosynthesis pathway, plant hormone signaling pathway, and starch sucrose metabolism pathway. PpSAUR73 also played an important role in IAA and ABA signal transduction pathways, it was speculated that it played an important role in the growth and development of peach trees.