ABSTRACT
Rho/Rac of plant (ROP) GTPases are plant-specific proteins that function as molecular switches, activated by guanine nucleotide exchange factors (GEFs) and inactivated by GTPase-activating proteins (GAPs). The bryophyte Marchantia polymorpha contains single copies of ROP (MpROP), GEFs [ROPGEF and SPIKE (SPK)] and GAPs [ROPGAP and ROP ENHANCER (REN)]. MpROP regulates the development of various tissues and organs, such as rhizoids, gemmae and air chambers. The ROPGEF KARAPPO (MpKAR) is essential for gemma initiation, but the functions of other ROP regulatory factors are less understood. This study focused on two GAPs: MpROPGAP and MpREN. Mpren single mutants showed defects in thallus growth, rhizoid tip growth, gemma development, and air-chamber formation, whereas Mpropgap mutants showed no visible abnormalities. However, Mpropgap Mpren double mutants had more severe phenotypes than the Mpren single mutants, suggesting backup roles of MpROPGAP in processes involving MpREN. Overexpression of MpROPGAP and MpREN resulted in similar gametophyte defects, highlighting the importance of MpROP activation/inactivation cycling (or balancing). Thus, MpREN predominantly, and MpROPGAP as a backup, regulate gametophyte development, likely by controlling MpROP activation in M. polymorpha.
Footnotes
Author contributions
Conceptualization: Y.S., K.I.; Methodology: Y.S., T.G., H.K.; Validation: Y.S., K.I.; Formal analysis: Y.S.; Investigation: Y.S., A.U., H.Y., T.G.; Resources: Y.S., K.I.; Data curation: Y.S., H.K., K.I.; Writing - original draft: Y.S., K.I.; Writing - review & editing: Y.S., A.U., H.Y., T.G., H.K., Y.K., H.F., K.I.; Visualization: Y.S., T.G.; Supervision: Y.K., H.F., K.I.; Project administration: Y.S., K.I.; Funding acquisition: Y.S., K.I.
Funding
This study was funded by Ministry of Education, Culture, Sports, Science and Technology (MEXT) KAKENHI grants (25119711, 15H01233 and 17H06472 to K.I.); Japan Society for the Promotion of Science (JSPS) KAKENHI grants (21J40092 to Y.S.; 15H04391 and 19H03247 to K.I.); the GteX Program (Japan Science and Technology Agency) (JPMJGX23B0 to K.I.); the Suntory Foundation for Life Sciences; the Yamada Science Foundation; and the Asahi Glass Foundation (K.I.).
Data availability
All relevant data can be found within the article and its supplementary information.
Special Issue
This article is part of the Special Issue 'Uncovering developmental diversity', edited by Cassandra Extavour, Liam Dolan and Karen Sears. See related articles at https://journals.biologists.com/dev/issue/151/20.
