Search

Introns can significantly affect gene expression in plants and many other eukaryotes in a variety of ways. Several types of gene regulation, both positive and negative, that involve plant introns are reviewed in this chapter. Some introns contain enhancer elements or alternative promoters, while many others elevate mRNA accumulation by a different process that has been named intron-mediated enhancement (IME). The introns involved in IME must be within transcribed sequences near the start of a gene and in their natural orientation to increase expression. The intron sequences involved are still poorly defined, and the mechanism of IME remains mysterious. A model of IME is presented in which introns increase transcript elongation.

A long term goal for this laboratory is to obtain a detailed understanding of the biochemical and genetic mechanisms that plants use to regulate the synthesis of the amino acid tryptophan (Last et al., 1992; Last, 1993). In addition to its role in the production of tryptophan for protein synthesis, this pathway gives rise to many indolic secondary metabolites, including the auxin, indole-3-acetic acid (Wright et al., 1991) and the Arabidopsis phytoallexin called camalexin (Tsuji et al., 1992). Thus, we anticipate that plants regulate the enzymes of tryptophan biosynthesis in response to requirements for both protein and secondary product biosynthesis.