A heat-shock inducible system for flexible gene expression in cereals

Sophie A Harrington,Anna E Backhaus,Annis Richardson,Cristobal Uauy,Samantha Fox,Christian Rogers,Philippa Borrill

doi:10.1186/s13007-020-00677-3

Abstract

BackgroundFunctional characterisation of genes using transgenic methods is increasingly common in cereal crops. Yet standard methods of gene over-expression can lead to undesirable developmental phenotypes, or even embryo lethality, due to ectopic gene expression. Inducible expression systems allow the study of such genes by preventing their expression until treatment with the specific inducer. When combined with the Cre-Lox recombination system, inducible promoters can be used to initiate constitutive expression of a gene of interest. Yet while these systems are well established in dicot model plants, like Arabidopsis thaliana, they have not yet been implemented in grasses.ResultsHere we present an irreversible heat-shock inducible system developed using Golden Gate-compatible components which utilises Cre recombinase to drive constitutive gene expression in barley and wheat. We show that a heat shock treatment of 38 °C is sufficient to activate the construct and drive expression of the gene of interest. Modulating the duration of heat shock controls the density of induced cells. Short durations of heat shock cause activation of the construct in isolated single cells, while longer durations lead to global construct activation. The system can be successfully activated in multiple tissues and at multiple developmental stages and shows no activation at standard growth temperatures (~ 20 °C).ConclusionsThis system provides an adaptable framework for use in gene functional characterisation in cereal crops. The developed vectors can be easily adapted for specific genes of interest within the Golden Gate cloning system. By using an environmental signal to induce activation of the construct, the system avoids pitfalls associated with consistent and complete application of chemical inducers. As with any inducible system, care must be taken to ensure that the expected construct activation has indeed taken place.

Highlights

Functional characterisation of genes using transgenic methods is increasingly common in cereal crops
Our aim was to have a construct that consisted of an inducible promoter that would drive expression of Cre recombinase upon application of the appropriate stimulus
The barley heat shock promoter HvHSP17 has been shown to be induced upon treatment for 2 h at 38 °C in wheat, with minimal background expression at lower temperatures [13]

Summary

Introduction

Functional characterisation of genes using transgenic methods is increasingly common in cereal crops. The gene is only expressed upon application of the required inducer These systems are useful when dealing with genes whose overexpression may be deleterious for the plant as well as to induce gene expression in specific tissues or at specific developmental times [6]. Chemicals such as β-estradiol [7, 8], ethanol [6, 9], and glucocorticoids such as dexamethasone [10, 11] have been used successfully to drive inducible transgenic systems in plants. Environmentally-driven systems have been established, utilising promoters which are induced under specific abiotic stresses, such as heat [12, 13], cold [14], or drought [15]

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