A conserved gene regulatory network controls root epidermal cell patterning in superrosid species

O_LIIn superrosid species, root epidermal cells differentiate into root hair cells and non-hair cells. In some superrosids, the root hair cells and non-hair cells are distributed randomly (Type I pattern) and in others, they are arranged in a position-dependent manner (Type III pattern). The model plant Arabidopsis (Arabidopsis thaliana) adopts the Type III pattern, and the gene regulatory network (GRN) that controls this pattern has been defined. However, it is unclear whether the Type III pattern in other species is controlled by a similar GRN as in Arabidopsis, and it is not known how the different patterns evolved. C_LIO_LIIn this study, we analyzed superrosid species Rhodiola rosea, Boehmeria nivea, and Cucumis sativus for their root epidermal cell patterns. Combining phylogenetics, transcriptomics, and cross-species complementation, we analyzed homologs of the Arabidopsis patterning genes from these species. C_LIO_LIWe identified R.rosea and B.nivea as Type III species and C.sativus as Type I species. We discovered substantial similarities in structure, expression, and function of Arabidopsis patterning gene homologs in R.rosea and B.nivea, and major changes in C.sativus. C_LIO_LIWe propose that in superrosids, diverse Type III species inherited the patterning GRN from a common ancestor, whereas Type I species arose by mutations in multiple lineages. C_LI