RHO GTPase of plants regulates polarized cell growth and cell division orientation during morphogenesis

Cell polarity-broadly defined as the asymmetric distribution of cellular activities and subcellular compo-nents within a cell-determines the geometry of cell growth and division during development. RHO GTPase proteins regulate the establishment of cell polarity and are conserved among eukaryotes. RHO of plant (ROP) proteins are a subgroup of RHO GTPases that are required for cellular morphogen-esis in plants. However, how ROP proteins modulate the geometry of cell growth and division during the morphogenesis of plant tissues and organs is not well understood. To investigate how ROP proteins function during tissue development and organogenesis, we characterized the function of the single -copy ROP gene of the liverwort Marchantia polymorpha (MpROP). M. polymorpha develops morpholog-ically complex three-dimensional tissues and organs exemplified by air chambers and gemmae, respec-tively. Mprop loss-of-function mutants form defective air chambers and gemmae, indicating ROP function is required for tissue development and organogenesis. During air chamber and gemma develop-ment in wild type, the MpROP protein is enriched to sites of polarized growth at the cell surface and ac-cumulates at the expanding cell plate of dividing cells. Consistent with these observations, polarized cell growth is lost and cell divisions are misoriented in Mprop mutants. We propose that ROP regulates both polarized cell growth and cell division orientation in a coordinated manner to orchestrate tissue develop-ment and organogenesis in land plants.

Automated summary

The RHO GTPase proteins, including ROP in plants, play a crucial role in regulating cell polarity and geometry during tissue development and organogenesis. The loss-of-function mutants of the ROP gene in M. polymorpha exhibit defective tissue development and organogenesis due to impaired polarized cell growth and cell division orientation.