Exogenous auxin-induced ENHANCER OF SHOOT REGENERATION 2 (ESR2) enhances femaleness of cucumber by activating theCsACS2gene

Abstract

Cucumber (Cucumis sativus L.) is a model for the study of sex differentiation in the last two decades. In cucumber, sex differentiation is mainly controlled by genetic material, but plant growth regulators can also influence or even change it. However, the effect of exogenous auxin application on cucumber sex differentiation is mostly limited in physiological level. In this study, we explored the effects of different exogenous auxin concentrations on the varieties with different mutant sex-controlling genotypes and found that there was a dosage effect of exogenous indole-3-acetic acid (IAA) on the enhancement of cucumber femaleness. Several ACC synthetase (ACS) family members could directly respond to the induction of exogenous IAA to improve endogenous ethylene synthesis, and this process can be independent on the previously identified sex-related ACC oxidase CsACO2. We further demonstrated that ENHANCER OF SHOOT REGENERATION 2 (ESR2), responding to the induction of exogenous auxin, could directly activate CsACS2 expression by combining the ERE cis-acting element regions in the promoter, and then increase endogenous ethylene content, which may induce femaleness. These findings reveal that exogenous auxin improves cucumber femaleness via inducing sex-controlling gene and promoting ethylene synthesis.

Novel Bisexual Flower Control Gene Regulates Sex Differentiation in Melon (Cucumis melo L.)

“…The monoecious-type bear male flowers on the main stem and female flowers on the axillary branches at the early stage, similar to the andromonoecious type, except that the latter bears hermaphrodite flowers on the axillary branches instead. Meanwhile, the androecious and gynoecious types bear only male and female flowers, respectively, while hermaphrodite produces only perfect flowers throughout the plant. − Therefore, in the last two decades, melons and cucumbers have been used as model plants for sex differentiation studies due to their diverse sexual forms and easy transition between the sexual types. , …”

“…4−6 Therefore, in the last two decades, melons and cucumbers have been used as model plants for sex differentiation studies due to their diverse sexual forms and easy transition between the sexual types. 7,8 Although melon has a very complex sexual pattern, its sexual differentiation can be summarized into two levels: pistil development involving female flowers (pistil) induction and simultaneous pistil and stamen formation involving unisexual/ bisexual flower development. 7,9 Three key sex-controlling genes have been identified in melon and cloned by classical genetics.…”

Molecular mapping of genomic regions and identification of possible candidate genes associated with gynoecious sex expression in bitter gourd

“…Feminizing effect in sex differentiation by promoting ethylene biosynthesis (Mibus & Tatlioglu, 2004;Liu et al, 2015;Niu et al, 2022)…”

“…Auxin exhibits feminizing effect, evident from transformation of male flower buds into female flower buds (Galun, 1962) and increased female flower rate in cucumber (Takahashi and Jaffe, 1984) upon exogenous IAA treatment. Exogenous IAA treatment resulted in up-regulation of ethylene biosynthesis-related genes, ACC synthases (CsACS1, CsACS2 and CsACS11) and ACC oxidases (CsACO1, CsACO3, and CsACO4) involved in sex determination in cucumber (Niu et al, 2022). Furthermore, presence of potential auxin-responsive elements (AREs) in the promoter region of CsACS1 and CsACS1G demonstrated the mutual cross-talk in between the auxin and ethylene in the development of female flowers in cucumber (Mibus and Tatlioglu, 2004;Knopf and Trebitsh, 2006).…”

“…Auxin Response Factors (ARFs) are crucial for the growth of pistils in Japanese Apricot (Song et al, 2015) and several auxin response elements (CpARFs) are reported to be involved in increased expression of ethylene signalling (CpETR) and biosynthesis (CpACS, CpACO) genes (Liu et al, 2015). In recent study, in cucumber, exogenous IAA treatment increased the transcription of ERF (CsESR2 and Csa4G630010) genes and one auxin response factor, ARF gene (Csa2G000030), suggesting that they may play regulatory roles in this crosstalk (Niu et al, 2022). Two auxin response factors CsARF13 and CsARF17 act as upstream regulators of Cucumber MADS-box 1 (CUM1) (Ran et al, 2018), AG homolog in cucumber which expresses specifically in the stamens and carpels (Perl-Treves et al, 1998).…”