Ionomic Screening of BRRI dhan84 Mutagenized Population Identifies Candidate Genes Underlying High Arsenic and Low...

Mutagenesis combined with ionomic profiling offers a powerful approach to explore the genetic basis of essential and toxic element accumulation in rice grain and to generate materials for marker-assisted breeding. However, large-scale ionomic screening has not previously been conducted in Bangladeshi rice germplasm. To isolate mutants with altered grain concentrations of iron, zinc (Zn), arsenic (As), and cadmium (Cd), we mutagenized BRRI dhan84 using ethyl methanesulfonate (EMS; 0.5% and 1%) and gamma rays (250, 300, 350, and 400 Gy). A total of 8503 M₂ plants were screened for brown rice ionome using inductively coupled plasma mass spectrometry (ICP-MS). Candidate mutants were selected based on robust Z-scores (|Z-scores| > 2) of the elements for individual plants, resulting in the isolation of 38 mutants. To validate the screening process, two mutants were characterized in detail: high grain As (osabcc1-3) and low grain Zn and Cd (oshma2-4). Whole genome sequencing of the mutants and the correlation between phenotype and genotype in the F₂ population indicated that OsABCC1 and OsHMA2 are likely the causal genes. The osabcc1-3 mutant carries a splice-site mutation at the exon-intron junction of OsABCC1, whereas oshma2-4 harbors a 3.3 kb insertion in OsHMA2. Notably, oshma2-4 exhibited similar growth and yield to BRRI dhan84 in a paddy field, suggesting its potential for breeding low-Cd rice. Together, these results demonstrate the effectiveness of ionomic screening in Bangladeshi rice for uncovering allelic variation controlling metal homeostasis and provide valuable genetic resources and physiological insights relevant to rice improvement.