Abstract
Fruit epidermal features such as the number and size of trichomes or spines are important fruit quality traits in cucumber production. Little is known about the molecular mechanisms underlying fruit spine formation in cucumber. Here, we report functional characterization of the cucumber CsMYB6 gene, which encodes a MIXTA-like MYB transcription factor that plays an important role in regulating fruit trichome development. Spatial-temporal expression analyses revealed high-level expression of CsMYB6 in the epidermis of cucumber ovaries during fruit spine initiation, which was similar to the expression of CsTRY, a homolog of the Arabidopsis TRY gene that also plays a key role in trichome development. Overexpression of CsMYB6 and CsTRY in cucumber and Arabidopsis revealed that CsMYB6 and CsTRY act as negative regulators of trichome initiation in both species, and that CsMYB6 acted upstream of CsTRY in this process. CsMYB6 was found to bind to the three MYB binding sites inside the promoter region of CsTRY, and protein-protein interaction assays suggested that CsTRY also directly interacted with CsMYB6 protein. The results also revealed conserved and divergent roles of CsMYB6 and its Arabidopsis homolog AtMYB106 in trichome development. Collectively, our results reveal a novel mechanism in which the CsMYB6-CsTRY complex negatively regulates fruit trichome formation in cucumber.
Highlights
Cucumber (Cucumis sativus L., 2n=2x=14) is one of the most economically important vegetable crops in the world,and it is the main vegetable grown in protected environments in China.The cucumber fruit, a pepo that develops from the ovary and receptacle, is covered with a thick cuticle, tubercules, and trichomes (Roth, 1977; Wang et al, 2015)
Spatial-temporal expression analyses revealed high-level expression of CsMYB6 in the epidermis of cucumber ovaries during fruit spine initiation, which was similar to the expression of CsTRY, a homolog of the Arabidopsis TRY gene that plays a key role in trichome development
A phylogenetic analysis of the cucumber MYB6 protein and the R2R3MYB proteins from Arabidopsis, snapdragon, petunia, tomato, and cotton, which have been shown to be involved in trichome development (Perez-Rodriguez et al, 2005; Jaffé et al, 2007; Jakoby et al, 2008; Pu et al, 2008; Li et al, 2012;Yoshimi et al, 2013), showed that it clustered within the MIXTA clade, which includes other known MIXTA-like transcription factors, such as AmMIXTA, AmMYBML1, GhMYB25, and GhMYB25-like, and was distinct from the MYBs, such as AtGL1, AtWER, and the cotton GL1-like MYB GhMYB109 (Fig. 1B)
Summary
Cucumber (Cucumis sativus L., 2n=2x=14) is one of the most economically important vegetable crops in the world,and it is the main vegetable grown in protected environments in China.The cucumber fruit, a pepo that develops from the ovary and receptacle, is covered with a thick cuticle, tubercules, and trichomes (or spines) (Roth, 1977; Wang et al, 2015). A trimeric complex that is composed of GLABRA1 (GL1; Oppenheimer et al, 1991), TRANSPARENT TESTA GLABRA1 (TTG1; Galway et al, 1994; Walker et al, 1999), and GLABRA 3/ENHANCER OF GLABRA3 (GL3/EGL3; Payne et al, 2000; Szymanski et al, 2000; Zhang et al, 2003) activates trichome initiation by promoting the expression of the genes GL2 and EGL2 (Larkin et al, 2003) In this complex, R3MYB transcription factors play vital roles in controlling trichome formation and development.One of these,TRY,is important because it can compete with GL1 for interaction with GL3/EGL3 and can suppress the initiation of trichome formation (Schellmann et al, 2002; Esch et al, 2003; Zhang et al, 2003)
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