Abstract
Brassinosteroids (BRs) are naturally occurring steroidal hormones that play diverse roles in various processes during plant growth and development. Thus, genetic manipulation of endogenous BR levels might offer a way of improving the agronomic traits of crops, including plant architecture and stress tolerance. In this study, we produced transgenic creeping bentgrass (Agrostis stolonifera L.) overexpressing a BR-inactivating enzyme, Arabidopsis thaliana BR-related acyltransferase 1 (AtBAT1), which is known to catalyze the conversion of BR intermediates to inactive acylated conjugates. After putative transgenic plants were selected using herbicide resistance assay, genomic integration of the AtBAT1 gene was confirmed by genomic PCR and Southern blot analysis, and transgene expression was validated by northern blot analysis. The transgenic creeping bentgrass plants exhibited BR-deficient phenotypes, including reduced plant height with shortened internodes (i.e., semi-dwarf), reduced leaf growth rates with short, wide, and thick architecture, high chlorophyll contents, decreased numbers of vascular bundles, and large lamina joint bending angles (i.e., erect leaves). Subsequent analyses showed that the transgenic plants had significantly reduced amounts of endogenous BR intermediates, including typhasterol, 6-deoxocastasterone, and castasterone. Moreover, the AtBAT1 transgenic plants displayed drought tolerance as well as delayed senescence. Therefore, the results of the present study demonstrate that overexpression of an Arabidopsis BR-inactivating enzyme can reduce the endogenous levels of BRs in creeping bentgrass resulting in BR-deficient phenotypes, indicating that the AtBAT1 gene from a dicot plant is also functional in the monocot crop.
Highlights
Steroidal plant hormones, brassinosteroids (BRs), play important roles for various processes during plant growth and development, which include seed germination, cell division and elongation, vascular differentiation, plant architecture, reproduction, senescence, and responses to stresses [1,2,3,4,5]
Non-transformed control plant died within 10 days after the herbicide treatment, whereas a transgenic bentgrass plant carrying an empty vector and all putative transformants exhibited resistance (Fig 1B). These results indicate that the BAR transgene is expressed in the transgenic plants
The Arabidopsis mutants were obtained by screening the FOX collection or activation-tagging lines, in which the mutation was caused by overexpression of the BR-related acyltransferase gene
Summary
Brassinosteroids (BRs), play important roles for various processes during plant growth and development, which include seed germination, cell division and elongation, vascular differentiation, plant architecture, reproduction, senescence, and responses to stresses [1,2,3,4,5]. The manipulation of endogenous levels of BRs has been widely used to improve the cultivation of crops, with effects on variables such as plant architecture, seed yield, and tolerance to stresses [6,7,8,9,10]. BRs affect many agricultural traits that influence grain yield in rice, including plant height, leaf angle, grain size, and tiller number [11,12,13]. The genetic manipulation of BR levels is suggested to offer a possibility for improving the agricultural traits of crops
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