OsARID3, an AT-rich Interaction Domain-containing protein, is required for shoot meristem development in rice

The shoot apical meristem (SAM) produces all of the plant's aerial organs. The SAM is established either during embryogenesis or experimentally in in vitro tissue culture. Although several factors including the Class I KNOTTED1-LIKE HOMEOBOX (KNOXI) proteins, auxin, and cytokinin are known to play essential roles in SAM development, the underlying mechanisms of SAM formation and maintenance are still largely not understood. Herein we demonstrate that OsARID3, a member of the rice (Oryza sativa) AT-rich Interaction Domain (ARID) family, is required for SAM development. Disruption of OsARID3 leads to a defective SAM, early seedling lethality, and impaired capacity of in vitro shoot regeneration. We show that the expression levels of several KNOXI genes and the biosynthetic genes for auxin and cytokinin are significantly altered in the Osarid3 mutant calli. Moreover, we determine that auxin concentrations are increased, whereas cytokinin levels are decreased, in Osarid3 calli. Furthermore, chromatin immunoprecipitation results demonstrate that OsARID3 binds directly to the KNOXI gene OSH71, the auxin biosynthetic genes OsYUC1 and OsYUC6, and the cytokinin biosynthetic genes OsIPT2 and OsIPT7. We also show through electrophoretic mobility shift assays that OsARID3 specifically binds to the AT-rich DNA sequences of the identified target genes. We conclude that OsARID3 is an AT-rich specific DNA-binding protein and that it plays a major role in SAM development in rice.