The Mechanism Forming the Cell Surface of Tip-Growing Rooting Cells Is Conserved among Land Plants

To discover mechanisms that controlled the growth of the rooting system in the earliest land plants, we identified genes that control the development of rhizoids in the liverwort Marchantia polymorpha. 336,000 T-DNA transformed lines were screened for mutants with defects in rhizoid growth, and a de novo genome assembly was generated to identify the mutant genes. We report the identification of 33 genes required for rhizoid growth, of which 6 had not previously been functionally characterized in green plants. We demonstrate that members of the same orthogroup are active in cell wall synthesis, cell wall integrity sensing, and vesicle trafficking during M. polymorpha rhizoid and Arabidopsis thaliana root hair growth. This indicates that the mechanism for constructing the cell surface of tip-growing rooting cells is conserved among land plants and was active in the earliest land plants that existed sometime more than 470 million years ago [1, 2]. •336,000 T-DNA lines and a genome assembly were generated in Marchantia polymorpha•33 genes required for rhizoid growth were identified•Six of the 33 genes were functionally characterized in plants for the first time•Genes belonging to these orthogroups were active in the first land plant roots Honkanen et al. identify 33 genes required for the growth of rhizoid rooting cells in the liverwort Marchantia polymorpha in a screen of 336,000 T-DNA-mutagenized lines and using a de novo genome assembly. Related genes were active during the development of the first plant rooting structures sometime before 460 million years ago.