Brassinosteroid Mediated Modulation in the Gene Expression Analysis of Genes Associated with Arsenic Uptake and Transport in Rice (Oryza sativa L.) for Effective Mitigation of Arsenic

The accumulation of arsenic in rice is several fold-higher compared to other cereal crops, posing a serious concern for the millions of people who rely on rice as their staple diet. Arsenic uptake and transportation in rice plants utilizes either silica (Si) or phosphate transporter. Recent studies have shown that the application of Brassinosteroids (BRs) could impede arsenic accumulation in hydrophonically grown rice plants. However, the effect of BRs has not been studied on expression of genes associated with arsenic accumulation and transportation in rice plants grown in naturally arsenic contaminated soil. Considering the growing importance of the role BRs in stress responses and protective role against toxicity of heavy metals in plants, we undertook a study to analyse genes associated with arsenic accumulation and transportation [OsHACs (OsHAC1;1 and OsHAC1;2), OsPht1, Lsi1, Lsi2, OsGrxs (OsGrx_C7 and OsGrx_C2.1), OsCLT1, OsNRAMP1, and OsABCC1] in 24-epibrassinolide (EBR), a BR, treated rice cv. Rajendra Kasturi grown in naturally arsenic contaminated soil. Interestingly, BRs mediated modulation of genes helps in lower accumulation of arsenic in flag leaves and seeds of rice plants. The higher enrichment of BES1, a major transcription factor (TF) in BR signaling pathway, was also observed in the promoter region of OsHAC1.1, Lsi1, Lsi2, and OsNRAMP1. In present investigation, we have clearly established that BRs treatment reduced (up to 50%) the uptake of arsenic, grown under naturally arsenic contaminated soil. Overall, a net positive impact on arsenic absorption in rice plant was achieved by BR treatment, emphasizing modulation of this trait by BR at a higher level in the hierarchical response system in plants. Gene expression analysis and reduced absorption of arsenic in rice seeds and straw in EBR-treated rice plants compared to mock treated provides a strong base for developing BR-based arsenic mitigation strategies in rice.