The Evolution of Transcriptional Regulation in the Viridiplantae and its Correlation with Morphological Complexity

Abstract

Since its origin from inorganic matter, biological life undoubtedly has gained complexity. Evidence of this can be found in the lineage of the Viridiplantae or Chlorobionta (“green plants”), represented by the extant diversity of green algae and land plants. The land plants, together with the multicellular animals, arguably represent the two most complex groups of organisms on earth. For both groups, a correlation between the observable morphological complexity and the regulatory networks principally controlling it has been hypothesized. Both groups of organisms not only independently evolved multicellularity, but also underwent ancestral whole genome duplication events that presumably acted as evolutionary playgrounds for the expansion of regulatory and morphological complexity. Within animals, multicellularity evolved once and most genome duplications occurred hundreds of millions of years ago. However, an entirely different scenario unfolds among the Viridiplantae: multicellularity evolved several times independently within the green lineage, and genome duplication is the rule rather than the exception and continues to be utilized. The most successful flavor of green multicellularity evolved within the last common ancestor of extant land plants and their sister group, the charophyte algae. In this chapter, we will review common complexity concepts, introduce and compare means to quantify them, and discuss how the evolution of morphological complexity, as measured by gene regulatory complexity, distinctively affected terrestrial plants and the predominantly aquatic green, red and brown algae.