Integrated Transcriptomics, Metabolomics, and Functional Analyses Uncover TaHma1-7b and Indole-3-carboxylic Acid as Key Regulators of Wheat Cadmium Detoxification.

Cadmium (Cd) threatens human health through wheat contamination. Previous studies lack insights into chloroplast-specific Cd detoxification mechanisms and metabolic regulators governing metal homeostasis. This study investigated contrasting Cd responses between two wheat genotypes: Cd-tolerant "H97" and Cd-sensitive "L193". Compared to Cd-compromised "L193", "H97" manifested through mitigated leaf chlorosis, optimized root architecture and photosynthetic capability, reduced reactive oxygen species accumulation, and lower grain Cd content. Moreover, "H97" exhibited significantly lower Cd accumulation within chloroplasts. Comparative transcriptomics and functional analyses identified TaHMA1-7B, a chloroplast-localized heavy metal ATPase, as a pivotal chloroplast Cd exporter, and its overexpression significantly enhanced rice tolerance against Cd toxicity. Metabolomic profiling coupled with exogenous application revealed that indole-3-carboxylic acid (ICA) conferred dose-dependent protection against Cd toxicity. Mechanistically, ICA significantly reduced leaf Cd concentrations and induced TaHMA1-7B expression. Collectively, our findings establish a chloroplast-centric detoxification pathway in which ICA potentially activates TaHMA1-7B-mediated Cd export from chloroplasts, thereby enhancing Cd tolerance.