Step by step evolution of Indeterminate Domain (IDD) transcriptional regulators: from algae to angiosperms.

Introduction: The Indeterminate Domain (IDD) proteins are a plant-specific subclass of C2H2 Zinc Finger transcription factors. Some of these transcription factors play roles in diverse aspects of plant metabolism and development, but the function of most of IDD genes is unknown and the molecular evolution of the subfamily has not been explored in detail.

Methods: In this study, we mined available genome sequences of green plants (Viridiplantae) to reconstruct the phylogeny and then described the motifs/expression patterns of IDD genes.

Key Results: We identified the complete set of IDD genes of 16 Streptophyta genomes. We found that IDD and its sister clade STOP arose by a duplication at the base of Streptophyta. Once on land, the IDD genes duplicated extensively, giving rise to at least ten lineages. Some of these lineages were lost in extant non-vascular plants and gymnosperms, but all of them were retained in angiosperms, duplicating profoundly in dicots and monocots and acquiring, at the same time, surprising heterogeneity in their C-terminal regions and expression patterns.

Conclusions: IDDs were present in the last common ancestor of Streptophyta. On land, IDDs duplicated extensively, leading to ten lineages. Later, IDDs were recruited by angiosperms where they diversified greatly in number, C-terminal and expression patterns. Interestingly, such diversification occurred during the evolution of novel traits of the plant body. This study provides a solid framework of the orthology relationships of green land plant IDD transcription factors, thus increasing the accuracy of orthologue identification in model and non-model species and facilitating the identification of agronomically important genes related to plant metabolism and development.