Abstract
Aluminum (Al) toxicity is a major constraint on crop productivity in acid soils, with barley being particularly susceptible. In our previous transcriptomic analysis, we identified HvAIR12 (AUXIN INDUCED IN ROOT CULTURES), a novel gene that is specifically induced by Al in the roots of the Al-tolerant Tibetan wild barley accession XZ16. In this study, we performed comprehensive physiological, transgenic, and molecular analyses to explore the role of HvAIR12 in Al tolerance. HvAIR12 encodes a plasma membrane-bound protein and is predominantly expressed in the roots, with its expression being strongly upregulated by Al exposure. Knockdown of HvAIR12 resulted in significantly reduced root growth and increased Al accumulation, whereas overexpression of HvAIR12 elevated H2O2 levels in the apoplast and promoted root growth—effects that were reversible by H2O2 scavengers. RNA sequencing further revealed that overexpression of HvAIR12 led to the transcriptional activation of several expansin genes, including HvEXPA4 and HvEXPB2. Functional characterization of HvEXPA4 transgenic lines and gene silencing experiments in HvAIR12-overexpressing backgrounds confirmed that HvEXPA4 is an essential downstream target of HvAIR12, mitigating Al toxicity by modulating cell wall components. This study uncovers the novel role of HvAIR12 in regulating apoplastic H2O2 levels and its interaction with other Al tolerance-related genes. Our findings highlight that HvAIR12 promotes Al tolerance through H2O2-mediated activation of HvEXPA4, forming a regulatory pathway critical for Al exclusion and root elongation under Al stress. These results providing valuable molecular insights and promising target genes for breeding more resilient cereal crops for cultivation in acid soils.
