Enhancing Brassinosteroid Signaling via Overexpression of Tomato (Solanum lycopersicum) SlBRI1 Improves Major Agronomic Traits.

Shuming Nie,Xiaofeng Wang,Siqi Lv,Shufen Wang,Shuhua Huang,Dandan Cheng,Qi Li,Jianwei Liu

doi:10.3389/fpls.2017.01386

Shuming Nie, Xiaofeng Wang + Show 6 more

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https://doi.org/10.3389/fpls.2017.01386

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Abstract

Brassinosteroids (BRs) play important roles in plant growth, development, and stress responses through the receptor, Brassinosteroid-insensitive 1 (BRI1), which perceives BRs and initiates BR signaling. There is considerable potential agricultural value in regulating BR signaling in crops. In this study, we investigated the effects of overexpressing the tomato (Solanum lycopersicum) BRI1 gene, SlBRI1, on major agronomic traits, such as seed germination, vegetative growth, fruit ethylene production, carotenoid accumulation, yield, and quality attributes. SlBRI1 overexpression enhanced the endogenous BR signaling intensity thereby increasing the seed germination rate, lateral root number, hypocotyl length, CO2 assimilation, plant height, and flower size. The transgenic plants also showed an increase in fruit yield and fruit number per plant, although the mean weight of individual fruit was reduced, compared with wild type. SlBRI1 overexpression also promoted fruit ripening and ethylene production, and caused an increase in levels of carotenoids, ascorbic acid, soluble solids, and soluble sugars during fruit ripening. An increased BR signaling intensity mediated by SlBRI1 overexpression was therefore positively correlated with carotenoid accumulation and fruit nutritional quality. Our results indicate that enhancing BR signaling by overexpression of SlBRI1 in tomato has the potential to improve multiple major agronomic traits.

Highlights

Brassinosteroids (BRs) are a group of steroid phytohormones that play important roles in plant growth, development, and stress responses (Zhu et al, 2013; Xia et al, 2015)
These results indicate that overexpression of SLBRI1 resulted in increased transcription and expression of SLBRI1 and caused a feedback-inhibition of BR biosynthetic genes, which showed decreased expression
We generated tomato SlBRI1-overexpressing plants, which we concluded showed increased BR signaling intensity based on the following evidence: SlBRI1 mRNA and protein levels in the overexpressing plants were significantly higher than in wild type (WT) (Figures 1B,C); the expression levels of the DWARF and CPD genes were markedly inhibited in the transgenic plants (Figures 1D,E) (He et al, 2005); and the hypocotyls and roots of the transgenic plants were significantly longer than WT (Figures 2E,F), which is known to closely correlate with the BR signaling intensity (Koka et al, 2000)

Summary

Introduction

Brassinosteroids (BRs) are a group of steroid phytohormones that play important roles in plant growth, development, and stress responses (Zhu et al, 2013; Xia et al, 2015). Brassinosteroids influence many important agronomic traits associated with growth, photosynthesis, architecture, and yield and crop quality. The application of BR analogs has been shown to promote plant growth, photosynthesis, fruit carotenoid accumulation, and quality attributes of fruit, while inhibiting BR biosynthesis with the compound Brassinazole has the opposite effect (Yu et al, 2004; Wu et al, 2008; Xia et al, 2009a). BRs increase photosynthetic capacity by activating RuBisCO activase (Xia et al, 2009a), and BR treatment induces ethylene production in fruit by inducing the expression of ethylene biosynthetic genes, thereby regulating ripening (Zhu et al, 2015). Exogenous BRs have been shown to enhance resistance of plants to abiotic and biotic stresses, such as drought, low and high temperatures, high salinity, and pathogen or nematode attack (Collins, 2007; Xia et al, 2009b; Ahammed et al, 2012; Xi et al, 2013)

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