Rice Chromatin Protein OsHMGB1 Is a Transcriptional Facilitator that Regulates Phosphate Homeostasis and Plant Growth [RNA-seq i]

Although phosphorus is one of the most important essential elements for plant growth and development, the epigenetic regulation of inorganic phosphate (Pi) signaling is poorly understood. In this study, we identified the high-mobility-group protein OsHMGB1 as a key regulator of phosphate homeostasis and plant growth in rice (Oryza sativa). OsHMGB1 expression is induced by Pi starvation and encodes a nucleus-localized protein. Relative to wild-type plants, Oshmgb1 mutant plants had lower Pi content in their leaves, whereas plants overexpressing OsHMGB1 had higher Pi content, indicating that OsHMGB1 positively regulates Pi accumulation. Transcriptome deep sequencing and chromatin immunoprecipitation followed by sequencing showed that OsHMGB1 regulated the expression of a series of phosphate starvation responsive (PSR) genes by binding to their promoters. Furthermore, Assay for Transposase-Accessible Chromatin followed by sequencing revealed that OsHMGB1 was involved in maintaining chromatin accessibility. Indeed, OsHMGB1 occupancy positively correlated with genome-wide chromatin accessibility and gene expression levels. Notably, we determined that OsHMGB1 interacted with RNA polymerase II to help regulate transcription, especially under low Pi conditions. Taken together, our results suggest that OsHMGB1 functions as a transcriptional facilitator, revealing a key epigenetic mechanism to regulate Pi homeostasis and fine-tune plant acclimation responses to Pi-limited environments. Overall design: Comparative gene expression profiling analysis of RNA-seq data for Oshmgb1 mutans and wild-type (WT) plants under HP (high Pi, 200µM) and LP (low Pi, 200µM) conditions.