Key message
The regulatory landscape of ethephon-accelerated fig ripening is revealed; flowers and receptacles exhibit opposite responses in anthocyanin accumulation; PG, PL and EXP are suggested key genes in fig softening.
Abstract
Ethephon is used to accelerate fig-fruit ripening for improvement of harvesting efficiency, but the underlying molecular mechanism is still unclear. To elucidate the detailed biological mechanism of ethylene-accelerated fig ripening, fruit in phase II (the lag phase on the double sigmoid growth curve) were treated with ethephon, and reached commercial ripeness 6 days earlier than the nontreated controls. Transcriptomes of flowers and the surrounding receptacles—which together make up the pseudocarp in fig fruit—were analyzed. There were 5189, 5818 and 2563 differentially expressed genes (DEGs) 2, 4 and 6 days after treatment (DAT) in treated compared to control fruit, screened by p-adjust < 0.05 and |log2(fold change) |≥ 2. The DEGs were significantly enriched in plant hormone metabolism and signal transduction, cell-wall modification, sugar accumulation and anthocyanin accumulation pathways. DEGs in the first three pathway categories demonstrated an overall similar expression change in flowers and receptacles, whereas DEGs in anthocyanin pigmentation revealed divergent transcript abundance. Specifically, in both flowers and receptacles, ethephon significantly upregulated 1-aminocyclopropane-1-carboxylate oxidase and downregulated most of the ethylene-response factor genes; polygalacturonase, pectate lyase and expansin were mainly upregulated; two acid beta-fructofuranosidases were upregulated. However, structural genes in the anthocyanin-synthesis pathway were mainly downregulated in female flowers 2 and 4 DAT, whereas they were upregulated in the receptacles. Our study reveals the regulatory landscape of the two tissues of fig fruit in ethylene-induced ripening; the differentially expressed pathways and genes provide valuable resources for the mining of target genes for crucial biological and commercial trait improvement.
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Data Availability
The RNA-Seq data have been deposited in NCBI (SRA accession: PRJNA606407).
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This work was supported by National Natural Science Foundation of China project NSFC [31372007].
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YC, YZ, and CZ designed the experiments. YC, YZ and JL conducted the experiments and analyzed the results. YC, YZ, MF, CZ, SC and HM prepared the manuscript. All authors have read and approved the manuscript for publication.
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Supplementary Fig. 1 Venn diagram showing the number of genes expressed in all samples and column diagram showing the number of genes expressed in each sample (JPG 1793 kb)
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Supplementary Fig. 2 Distribution characteristics of TPM values for the differentially expressed genes (DEGs) related to auxin (JPG 1655 kb)
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Supplementary Fig. 3 Heat map of 61 cell-wall-related differentially expressed genes (DEGs) with higher TPM values (greater than 100 in at least one of the 14 samples) (JPG 12351 kb)
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Supplementary Fig. 7 KEGG enrichment analysis of differentially expressed genes (DEGs) after ethephon treatment. Richness factor represents the ratio of the number of unigenes enriched in a particular pathway to the number of annotated genes (background number) in that pathway. The larger the richness factor, the greater the degree of enrichment. The size of the dots indicates the number of unigenes enriched in a particular pathway (JPG 10,155 kb)
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Supplementary Table 3 TPM value of ethylene-related differentially expressed genes (DEGs) in the 14 samples (DOCX 22 kb)
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Supplementary Table 4 Expression changes of ABA-, cytokinin- and gibberellin-related differentially expressed genes (DEGs) in the 14 samples (DOCX 24 kb)
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Supplementary Table 5 Expression changes of cell-wall-related differentially expressed genes (DEGs) in the 14 samples (DOCX 90 kb)
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Cui, Y., Zhai, Y., Flaishman, M. et al. Ethephon induces coordinated ripening acceleration and divergent coloration responses in fig (Ficus carica L.) flowers and receptacles. Plant Mol Biol 105, 347–364 (2021). https://doi.org/10.1007/s11103-020-01092-x
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DOI: https://doi.org/10.1007/s11103-020-01092-x