Functions of ABC Transporter OsARG1 in Rice Heading Date Regulation

Heading date is a critical agronomic trait influencing rice yield and quality, regulated by complex networks involving histone-modifying enzymes, transcription factors, protein kinases, florigens, and phytochromes. While ATP-binding cassette (ABC) transporters are known for their roles in substrate transport, their functions in heading date regulation remain unclear. This study investigates the role of the ABC transporter gene OsARG1 in the regulation of rice heading date, which will provide evidence for enriching the heading date regulation network.

A comparative analysis was conducted between wild-type Nipponbare and the osarg1 mutant. Key agronomic traits, including heading date, plant height, tiller number, and panicle length, were assessed. Chlorophyll contents in leaf of Nipponbare (WT), albino leaf (WL), yellow-green leaf (YL) and green leaf (GL) of osarg1 were measured. Metal element contents such as cobalt, nickel, calcium, magnesium and iron in WT, WL, YL and GL were determined by ICP-MS. Hormone profiling, transcriptome sequencing, and integrative analysis were performed on WT, WL and GL to explore the regulatory function of OsARG1.

The osarg1 mutant exhibited an earlier heading date than wild-type in both Guiyang and Changchun. It also showed reduced plant height, tiller number, and panicle length. Chlorophyll levels in WL and YL were significantly lower, accompanied by disrupted metal element homeostasis. Hormonal analysis revealed elevated levels of gibberellins, auxin-related, and cytokinin-related hormones in GL and WL, particularly in WL. Transcriptome analysis identified 2 001 and 6 555 differentially expressed genes (DEGs) in GL_vs_WT and WL_vs_WT comparisons, respectively. Over 20 heading date-associated genes, including Hd3a, OsMADS14, and chromatin methyltransferase genes, were differentially expressed. GO and KEGG analyses of DEGs from GL vs WT comparison highlighted enrichment in pathways related to metabolism, development, and environmental responses. Integrated transcriptomic and hormonal analysis suggested that OsARG1 may influence gibberellin and cytokinin levels by modulating diterpene and zeatin metabolism and hormone signaling pathways. Expression levels of the selected genes by qRT-PCR were consistent with the transcriptome data, validating the transcriptomic findings.

The osarg1 mutant heads earlier than the wild-type, with OsARG1 likely regulating heading date through modulating the expression of heading date related genes. Additionally, OsARG1 plays roles in maintaining chlorophyll content and metal element (such as nickel, iron, and magnesium) balance in rice leaves.