SummaryStreptophytes colonized the land some time before 470 million years ago [1, 2, 3]. The colonization coincided with an increase in morphological and cellular diversity [4, 5, 6, 7]. This increase in diversity is correlated with a proliferation in transcription factors encoded in genomes [8, 9, 10]. This suggests that gene duplication and subsequent diversification of function was instrumental in the generation of land plant diversity. Here, we investigate the diversification of the streptophyte-specific Lotus japonicus ROOTHAIRLESS LIKE (LRL) transcription factor (TF) [11, 12] subfamily of basic loop helix (bHLH) proteins by comparing gene function in early divergent and derived land plant species. We report that the single Marchantia polymorpha LRL gene acts as a general growth regulator required for rhizoid development, a function that has been partially conserved throughout multicellular streptophytes. In contrast, the five relatively derived Arabidopsis thaliana LRL genes comprise two antagonistically acting groups of differentially expressed genes. The diversification of LRL genes accompanied the evolution of an antagonistic regulatory element controlling root hair development.

pictures of the Marchantia wild-type and Mpfer mutant strains were accidently inverted during the Graphical Abstract assembly. Marchantia wild-type strain should have been depicted by the thallus with long intact rhizoids, while Mpfer mutant strain should have been represented by the picture of the thallus with almost no visible intact rhizoids due to their loss of cell-wall integrity. This picture inversion has now been corrected online. We present our apologies for this error and for any confusion that may have resulted.

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Gene duplication is a major driver for the increase of biological complexity. The divergence of newly duplicated paralogs may allow novel functions to evolve, while maintaining the ancestral one. Alternatively, partitioning the ancestral function among paralogs may allow parts of that role to follow independent evolutionary trajectories. We studied the () locus, which contains three paralogs that have evolved through two independent events of gene duplication, and which underlies repeated events of leaf shape evolution within the Brassicaceae In particular, we took advantage of the presence of three potentially functional paralogs in to investigate the extent of functional divergence among them. We demonstrate that the copies control growth in different areas of the leaf. Consequently, the copies that are retained active in the different Brassicaceae lineages contribute to define the leaf dissection pattern. Our results further illustrate how successive gene duplication events and subsequent functional divergence can increase trait evolvability by providing independent evolutionary trajectories to specialized functions that have an additive effect on a given trait.