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

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: Correlation analysis of RNA-seq data (gene expression profile) and ATAC-seq data (genome-wide accessibility) for Oshmgb1 mutans and wild-type (WT) plants under HP conditions.

尽管磷是植物生长发育过程中至关重要的必需元素之一，但目前针对无机磷酸（Pi）信号通路的表观遗传调控机制仍知之甚少。本研究将高迁移率族蛋白OsHMGB1鉴定为水稻（Oryza sativa）中磷酸盐稳态与植物生长的关键调控因子。OsHMGB1的表达受Pi饥饿诱导，其编码定位于细胞核的蛋白质。与野生型植株相比，Oshmgb1突变体的叶片Pi含量更低，而过表达OsHMGB1的植株叶片Pi含量更高，表明OsHMGB1可正向调控Pi积累。转录组深度测序与染色质免疫共沉淀测序结果显示，OsHMGB1可通过结合一系列磷饥饿响应（phosphate starvation responsive, PSR）基因的启动子调控其表达。进一步的转座酶可及性测序（Assay for Transposase-Accessible Chromatin followed by sequencing, ATAC-seq）分析表明，OsHMGB1参与维持染色质可及性。事实上，OsHMGB1的基因组结合位点与全基因组染色质可及性及基因表达水平呈显著正相关。值得注意的是，本研究发现OsHMGB1可与RNA聚合酶Ⅱ相互作用，协助调控转录过程，尤其在低Pi培养条件下。综上，本研究结果表明OsHMGB1作为转录辅助因子发挥功能，揭示了调控磷酸盐稳态并微调植物对低Pi环境的适应响应的关键表观遗传机制。

整体实验设计：对高磷（HP）条件下的Oshmgb1突变体与野生型（WT）植株，开展RNA-seq数据（基因表达谱）与ATAC-seq数据（全基因组染色质可及性）的相关性分析。