A conserved nuclear factor YC subunit, NF-YC3, is essential for arbuscule development.

Establishing reciprocal symbiosis with arbuscular mycorrhizal (AM) fungi is an important evolutionary strategy of most terrestrial plants to adapt to environmental stresses, especially phosphate (Pi) deficiencies. Identifying the key genes essential for AM symbiosis in plants and dissecting their functional mechanisms will be helpful for the breeding of new crop varieties with enhanced nutrient uptake efficiency. Here, we report a nuclear factor YC subunit-encoding gene, OsNF-YC3, whose expression is specifically induced in arbuscule-containing cells, plays an essential role in AM symbiosis. Knockout of OsNF-YC3 resulted in stunted arbuscule morphology and substantially decreased P accumulation, while overexpressing OsNF-YC3 enhanced mycorrhization and Pi uptake efficiency. OsNF-YC3 is directly regulated by OsPHRs, the major regulators of Pi starvation responses. Chromatin immunoprecipitation sequencing analysis uncovered multiple genes with crucial roles in arbuscule development as its potential downstream targets, including the AM-specific Pi transporter gene OsPT11. OsNF-YC3 can form a heterotrimer with the other two NF-Y subunits, OsNF-YA11 and OsNF-YB11, in yeast. Loss of OsNF-YA11 function also severely impaired arbuscule development in its mutants. Overall, our results highlight an essential role of OsNF-YC3 and its potential interacting NF-Y subunit, OsNF-YA11, in regulating AM symbiosis and arbuscule development.