Abstract
Sex differentiation of flower buds is an important developmental process that directly affects fruit yield of cucumber (Cucumis sativus L.). Plant hormones, such as gibberellins (GAs) and ethylene can promote development of male and female flowers, respectively, however, the regulatory mechanisms of GA-induced male flower formation and potential involvement of ethylene in this process still remain unknown. In this study, to unravel the genes and gene networks involved in GA-regulated cucumber sexual development, we performed high throughout RNA-Seq analyses that compared the transcriptomes of shoot tips between GA3 treated and untreated gynoecious cucumber plants. Results showed that GA3 application markedly induced male flowers but decreased ethylene production in shoot tips. Furthermore, the transcript levels of M (CsACS2) gene, ethylene receptor CsETR1 and some ethylene-responsive transcription factors were dramatically changed after GA3 treatment, suggesting a potential involvement of ethylene in GA-regulated sex expression of cucumber. Interestingly, GA3 down-regulated transcript of a C-class floral homeotic gene, CAG2, indicating that GA may also influence cucumber sex determination through an ethylene-independent process. These results suggest a novel model for hormone-mediated sex differentiation and provide a theoretical basis for further dissection of the regulatory mechanism of male flower formation in cucumber.Statement: We reveal that GA can regulate sex expression of cucumber via an ethylene-dependent manner, and the M (CsACS2), CsETR1, and ERFs are probably involved in this process. Moreover, CAG2, a C-class floral homeotic gene, may also participate in GA-modulated cucumber sex determination, but this pathway is ethylene-independent.
Highlights
Cucumber (Cucumis sativus L.) is a typical monoecious plant with distinct male and female flowers, and has been served as a model system for studying physiological and molecular aspects of sex determination in plants (Malepszy and NiemirowiczSzczytt, 1991; Bai and Xu, 2013)
To verify the effect of GA on sex expression of cucumber, a gynoecious cucumber line 13-3B was treated with GA3 and the sex of flowers on each node was recorded until anthesis of the flowers on node 25 of the main stems
It is well known that ethylene can control sex determination of cucumber (Malepszy and Niemirowicz-Szczytt, 1991; Bai and Xu, 2013)
Summary
Cucumber (Cucumis sativus L.) is a typical monoecious plant with distinct male and female flowers, and has been served as a model system for studying physiological and molecular aspects of sex determination in plants (Malepszy and NiemirowiczSzczytt, 1991; Bai and Xu, 2013). During the early stages of cucumber flower development, both stamen primordia and carpel primordia are initiated, sex differentiation occurs just after the hermaphroditic stage, subsequently, female or male flower is formed and developed through the selective developmental arrest of stamen or carpel, respectively (Bai et al, 2004). F (CsACS1G) and M (CsACS2) genes encoding two ACC synthases (key enzymes in ethylene biosynthetic pathway) govern female sex expression in cucumber, and the F gene promotes female flower development (Trebitsh et al, 1997; Mibus and Tatlioglu, 2004; Knopf and Trebitsh, 2006), while the M gene inhibits stamen development in flower buds (Yamasaki et al, 2001, 2003; Saito et al, 2007; Li et al, 2009, 2012). The interaction of F, M, and A genes eventually determines various sexual phenotypes of cucumber
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