Dual Roles of in Modulating Rice Root Morphology and Affecting Arbuscular Mycorrhizal Symbiosis

Several angiosperm () genes, including tomato and rice are induced during arbuscular mycorrhizal (AM) symbiosis, but their functions remain largely unclear. Recently, tomato was suggested to negatively regulate arbuscule incidence decreasing auxin levels in colonized cells. In this study, by acquiring rice :β-glucuronidase () transgenic plants and generating mutants CRISPR/Cas9 technique, the roles of in modulating rice root morphology and affecting AM symbiosis were investigated through time course experiments. Unlike , showed asymbiotic expression in rice young lateral roots, and its mutation resulted in a "shallow" root architecture. Such root morphological change was also observed under symbiotic condition and it likely promoted AM fungal colonization, as the mutants exhibited higher colonization levels and arbuscule incidence than wild-type at early stages. Similar to , showed symbiotic expression in cortical cells that have formed mature arbuscules. At late stages of symbiosis, mutants showed elongated cortical cells and larger arbuscules than wild-type, indicating elevated auxin level in the colonized cells. Together, these results revealed both asymbiotic and symbiotic roles of in modulating rice root architecture and controlling auxin levels in arbusculated cells, which further affected colonization rate and arbuscule phenotype.