Functional genomics: probing plant gene function and expression with transposons

Abstract

Transposable elements provide a convenient and flexible means to disrupt plant genes, so allowing their function to be assessed. By engineering transposons to carry reporter genes and regulatory signals, the expression of target genes can be monitored and to some extent manipulated. Two strategies for using transposons to assess gene function are outlined here: First, the PCR can be used to identify plants that carry insertions into specific genes from among pools of heavily mutagenized individuals (site-selected transposon mutagenesis). This method requires that high copy transposons be used and that a relatively large number of reactions be performed to identify insertions into genes of interest. Second, a large library of plants, each carrying a unique insertion, can be generated. Each insertion site then can be amplified and sequenced systematically. These two methods have been demonstrated in maize, Arabidopsis, and other plant species, and the relative merits of each are discussed in the context of plant genome research.

Figure 1

Examples of reporter gene expression (blue) in various gene trap and enhancer trap lines illustrating cell type-specific expression, expression in prepatterns, and subcellular gene trap localization. Seedlings were grown in continuous light for 7 days, stained for GUS activity, cleared in 70% ethanol, and mounted for differential interference contrast microscopy in 25% glycerol (12, 42). (A) Nuclear staining (arrow) in roots from heterozygous prolifera/+ plants. (B) Meristem staining in the shoot. (C) GUS expression at the basal boundaries of leaf primordia. (D) GUS expression in columella initials in the root. (E) GUS expression in root cap cells. (F) GUS expression in immature trichomes. (G) GUS expression in trichome accessory cells.