Intron-Mediated Enhancement: A Tool for Heterologous Gene Expression in Plants?

Miriam Laxa

doi:10.3389/fpls.2016.01977

Abstract

Many plant promoters were characterized and used for transgene expression in plants. Even though these promoters drive high levels of transgene expression in plants, the expression patterns are rarely constitutive but restricted to some tissues and developmental stages. In terms of crop improvement not only the enhancement of expression per se but, in particular, tissue-specific and spatial expression of genes plays an important role. Introns were used to boost expression in transgenic plants in the field of crop improvement for a long time. However, the mechanism behind this so called intron-mediated enhancement (IME) is still largely unknown. This review highlights the complexity of IME on the levels of its regulation and modes of action and gives an overview on IME methodology, examples in fundamental research and models of proposed mechanisms. In addition, the application of IME in heterologous gene expression is discussed.

Highlights

For a long time, gene regulation has mainly been attributed to cis-elements in the promoter regions of genes
intron-mediated enhancement (IME) affects all levels of gene expression, but the strongest effect of IME was shown on the levels of post-transcription and translation (Rose and Last, 1997; Samadder et al, 2008)
Supporting this theory, Rose and Last (1997) showed that an increase in mRNA accumulation is depending on the presence of the AtPAT1 intron, while there was no change in the rate of transcription when compared to the intronless construct (Rose and Last, 1997)

Summary

INTRODUCTION

Gene regulation has mainly been attributed to cis-elements in the promoter regions of genes. IME affects all levels of gene expression, but the strongest effect of IME was shown on the levels of post-transcription and translation (Rose and Last, 1997; Samadder et al, 2008). A detectable effect on the translation level relative to the post-transcriptional level was only shown for a few introns (Mascarenhas et al, 1990; Lu et al, 2008; Samadder et al, 2008). An intron targeting the level of either post-transcription or translation can enhance expression of a gene on both levels, while an intron targeting the RNA level can impact either tissue specificity or the level of gene expression This is very important because some introns not enhance expression but restrict expression to specific tissues (Liao et al, 2013). The major limit of gene expression in transgenic plants is the low yield of final protein (Desai et al, 2010)

METHODOLOGY OF STUDYING IME

CONCLUSION