Abstract
The number and proportion of female flowers per plant can directly influence the yield and economic benefits of cucurbit crops. Ethephon is often used to induce female flowers in cucurbits. However, the mechanism through which it affects floral sex differentiation in pumpkin is unknown. We found that the application of ethephon on shoot apical meristem of pumpkin at seedling stage significantly increased the number of female flowers and expedited the appearance of the first female flower. These effects were further investigated by transcriptome and hormone analyses of plants sprayed with ethephon. A total of 647 differentially expressed genes (DEGs) were identified, among which 522 were upregulated and 125 were downregulated. Gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) analysis indicated that these genes were mainly enriched in plant hormone signal transduction and 1-aminocyclopropane-1-carboxylate oxidase (ACO). The results suggests that ethylene is a trigger for multiple hormone signaling, with approximately 4.2% of the identified DEGs involved in ethylene synthesis and multiple hormone signaling. Moreover, ethephon significantly reduced the levels of jasmonic acid (JA), jasmonoyl-L-isoleucine (JA-ILE), and para-topolin riboside (pTR) but increased the levels of 3-indoleacetamide (IAM). Although the level of 1-aminocyclopropanecarboxylic acid was not changed, the expression of ACO genes, which code for the enzyme catalyzing the key rate-limiting step in ethylene production, was significantly upregulated after ethephon treatment. The results indicate that the ethephon affects the transcription of ethylene synthesis and signaling genes, and other hormone signaling genes, especially auxin responsive genes, and modulates the levels of auxin, jasmonic acid, and cytokinin (CK), which may together contribute to femaleness.
Highlights
Pumpkin (Cucurbita moschata Duch.) is cultivated worldwide and is popular for its high nutritional and medicinal value (Lu et al, 2019)
A transcription factor, CsWIP1, which is negatively correlated with the formation of female flowers, could repress the expression of CsACO2 by binding to its promoter (Chen et al, 2016). These findings suggest that aminocyclopropane-1-carboxylate oxidase (ACO) is indispensable for the development of female flowers
Ethephon treatment significantly expedited the appearance of the first female flower from node 13.29 ± 1.89 to node 8.29 ± 1.50
Summary
Pumpkin (Cucurbita moschata Duch.) is cultivated worldwide and is popular for its high nutritional and medicinal value (Lu et al, 2019). Pumpkin is a typical material for exploration of floral sex differentiation. The sex differentiation in the flowers of pumpkin includes three stages. Male flowers appear at the base nodes of the plant, and almost no Ethephon-Induced Femaleness in Pumpkin female flowers are generated at this stage. Female flowers alternate with male flowers; usually, one female flower appears after several male flowers. In the third stage, which occurs at the end of the blooming season, female flowers appear continuously, but these are not suitable for generating fruits. Male flowers are much more abundant than female flowers in pumpkin. For higher yield, it is necessary to have more female flowers per plant
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