Genome-Wide Transcriptional Profiling and Functional Analysis Reveal That OsPHT4;4 Is Critical for the Growth and Development of Rice

Phosphorus (P) is an essential macronutrient required for various vital processes in crop growth and development, including signal transduction, CO₂ fixation, and photosynthetic phosphorylation. Phosphate transporters (PHTs) in plants play critical roles in the uptake, distribution, and internal transport of Phosphate (Pi). Among these transporters, the PHT4 family is widely distributed across plant species; however, the specific functions of many members within this family remain to be fully elucidated. This study focuses on unraveling the function of OsPHT4;4 in Pi utilization and photoprotection. The findings demonstrate that OsPHT4;4 acts as a low-affinity Pi transporter localized to the chloroplast membrane and reveal predominant expression of OsPHT4;4 in leaves, with peak expression during tillering and clear induction by light, exhibiting circadian rhythmicity. The ospht4;4 mutants display stunted growth. Transcriptomic analysis comparing ospht4;4 mutants and wild-types (WT) identified 1482 differentially expressed genes (DEGs), including 729 upregulated genes and 753 downregulated genes. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis reveals enrichment DEGs related to photosynthesis-antenna proteins, carbohydrate metabolism, and phenylpropanoid biosynthesis. These findings suggest that OsPHT4;4 plays crucial roles not only in photosynthesis but also in plant defense as an integral component involved in Pi metabolism.