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LEAFY Evolution
It is generally believed that redundancy across gene copies allows for the evolution of novel function in proteins. However, it is less clear how single-copy genes with crucial function may evolve. Sayou et al. (p. 645, published online 16 January; see the Perspective by Kovach and Lamb) examined the evolution of the essential plant transcription factor LEAFY, which is generally found as a single-copy gene. LEAFY homologs in taxa representing the major evolutionary branches of the land plants and algae exhibited three classes of LEAFY binding sites. Structural analysis identified amino acid changes in the proteins, that were responsible for contacts with specific DNA motifs and allowed the likely effects of specific amino acid changes over the evolution of land plants to be resolved.
Abstract
Transcription factors (TFs) are key players in evolution. Changes affecting their function can yield novel life forms but may also have deleterious effects. Consequently, gene duplication events that release one gene copy from selective pressure are thought to be the common mechanism by which TFs acquire new activities. Here, we show that LEAFY, a major regulator of flower development and cell division in land plants, underwent changes to its DNA binding specificity, even though plant genomes generally contain a single copy of the LEAFY gene. We examined how these changes occurred at the structural level and identify an intermediate LEAFY form in hornworts that appears to adopt all different specificities. This promiscuous intermediate could have smoothed the evolutionary transitions, thereby allowing LEAFY to evolve new binding specificities while remaining a single-copy gene.
