The Plasmodesmal Protein OsGER4 is Involved in Auxin Mediated Crown Root Development in Rice

In rice (Oryza sativa L.), the root system plays different essential roles, from water and nutrient uptake to responding to environmental signals. The mechanisms underlying root development are complex and involve many phytohormones, of which auxin is the most important. This study investigates the involvement of OsGER4, a putative Germin-like protein, in auxin-mediated crown root development in rice. The expression study of OsGER4 in the crl1 mutant confirms that OsGER4 is connected to the CRL1 signaling pathway- a master regulator for crown root development. Transgenic rice carrying the promGER4::GUS reporter gene revealed that OsGER4 is mainly expressed in the initiation and emergence zone of the crown and lateral root, such as epidermal cell, vasculature, and primordia under auxin treatment condition. Moreover, fewer crown roots of osger4 knockout mutant lines than the wild type under auxin treatment suggests that OsGER4 might function as a regulator limiting auxin flux to root growth regions under stress conditions. Besides, protein localization experiments confirmed that OsGER4 localizes to plasmodesmata, which are intercellular channels that could facilitate auxin transport. Our findings suggest that OsGER4 might play a substantial role in regulating plasmodesmata conformation to regulate auxin flow resulting in crown root developmental in rice under stress conditions.