OsARP6 Is Involved in Internode Elongation by Regulating Cell-Cycle-Related Genes

The SWR1 complex (SWR1-C) is important for the deposition of histone variant H2A.Z into chromatin to regulate gene expression. Characterization of SWR1-C subunits in Arabidopsis thaliana has revealed their role in variety of developmental processes. Oryza sativa actin related protein 6 (OsARP6) is a subunit of rice SWR1-C. Its role in rice plant development is unknown. Here, we examined the subcellular localization, expression patterns, and loss of function phenotypes for this protein and found that OsARP6 is a nuclear localized protein, and is broadly expressed. OsARP6 interacted with OsPIE1, a central ATPase subunit of rice SWR1-C. The osarp6 knockout mutants displayed pleiotropic phenotypic alterations in vegetative and reproductive traits, including semi-dwarf phenotype, lower tillers number, short leaf length, changes in spikelet morphology, and seed abortion. Microscopic thin sectioning of the top internode revealed that the dwarf phenotype of osarp6 was due to reduced number of cells rather than reduced cell length. The altered transcript level of genes involved in cell division suggested that OsARP6 affects cell cycle regulation. In addition, H2A.Z levels were reduced at the promoters and transcription start sites (TSS) of the regulated genes in osarp6 plants. Together, these results suggest that OsARP6 is involved in rice plant development, and H2A.Z deposition.