Green prickly ash (Zanthoxylum armatum) and red prickly ash (Zanthoxylum bungeanum) fruit have unique flavor and aroma characteristics that affect consumers’ purchasing preferences. However, differences in aroma components and relevant biosynthesis genes have not been systematically investigated in green and red prickly ash. Here, through the analysis of differentially expressed genes (DEGs), differentially abundant metabolites, and terpenoid biosynthetic pathways, we characterize the different aroma components of green and red prickly ash fruits and identify key genes in the terpenoid biosynthetic pathway. Gas chromatography-mass spectrometry (GC-MS) was used to identify 41 terpenoids from green prickly ash and 61 terpenoids from red prickly ash. Piperitone was the most abundant terpenoid in green prickly ash fruit, whereas limonene was most abundant in red prickly ash. Intergroup correlation analysis and redundancy analysis showed that HDS2, MVK2, and MVD are key genes for terpenoid synthesis in green prickly ash, whereas FDPS2 and FDPS3 play an important role in the terpenoid synthesis of red prickly ash. In summary, differences in the composition and content of terpenoids are the main factors that cause differences in the aromas of green and red prickly ash, and these differences reflect contrasting expression patterns of terpenoid synthesis genes.

Background: AP2/ERF is a large family of plant transcription factor proteins that play essential roles in signal transduction, plant growth and development, and responses to various stresses. The AP2/ERF family has been identified and verified by functional analysis in various plants, but so far there has been no comprehensive study of these factors in Chinese prickly ash. Phylogenetic, motif, and functional analyses combined with transcriptome analysis of Chinese prickly ash fruits at different developmental stages (30, 60, and 90 days after anthesis) were conducted in this study. Results: The analysis identified 146 ZbAP2/ERF genes that could be classified into 15 subgroups. The motif analysis revealed the presence of different motifs or elements in each group that may explain the functional differences between the groups. ZbERF13.2, ZbRAP2-12, and ZbERF2.1 showed high levels of expression in the early stages of fruit development. ZbRAP2-4, and ZbERF3.1 were significantly expressed at the fruit coloring stage (R2 and G2). ZbERF16 were significantly expressed at fruit ripening and expression level increased as the fruit continued to develop. Relative gene expression levels of 6 representative ZbAP2/ERFs assessed by RT-qPCR agreed with transcriptome analysis results. Conclusions: These genes identified by screening can be used as candidate genes that affect fruit development. The results of the analysis can help guide future genetic improvement of Chinese prickly ash and enrich our understanding of AP2/ERF transcription factors and their regulatory functions in plants.

Apomixis is a form of reproduction that does not involve the fertilization of female gametes by male gametes but instead involves the production of offspring directly from the female parent. The offspring of apomixis are genetically identical to the female parent and inherit its traits. Therefore, apomixis has great potential for application to agricultural genetic breeding. However, it remains unclear whether apomictic species require pollination, and the impacts of pollination on such species are poorly understood. We investigated the effects of pollination on the apomictic species Zanthoxylum bungeanum Maxim. by analyzing its fertilization process, assembling its transcriptome, and measuring hormone concentrations, fruit setting rate and gene expression levels. Transcriptome sequencing of pollinated and unpollinated fruits resulted in a total of 69,131 PacBio reads. Of these, 7102 genes were up-regulated and 6491 genes were down-regulated. Analysis of the differentially expressed genes (DEGs) and construction of a weighted gene co-expression network showed that many DEGs were involved in plant hormone signal transduction, suggesting that hormonal signaling during development differs between pollinated and unpollinated fruit. The germination rate of Z. bungeanum pollen in vitro was only 11%, and pollen could not germinate in the embryo sac to complete fertilization. Although pollination did not enable Z. bungeanum to complete the sexual reproduction process, it significantly increased abscisic acid (ABA) concentration and fruit setting rate. Spraying 100 μg l⁻¹ ABA also significantly increased the fruit setting rate. Therefore, ABA appears to be a key factor in the regulation of fruit setting in apomictic Z. bungeanum. Based on these results, we suggest that some male plants be cultivated in Z. bungeanum plantations or exogenous ABA be sprayed to increase the likelihood of pollination and thereby increase the fruit setting rate.