Tandemly duplicated HmALS3 gene cluster mediates aluminum hyperaccumulation via a heteromeric transport complex in...

Aluminum (Al) toxicity in acidic soils severely constrains global agricultural productivity. While Hydrangea macrophylla is a model Al-hyperaccumulator, the molecular mechanisms governing its high-capacity internal sequestration remain elusive. Here, we identify an Al-induced, tandemly duplicated gene cluster, HmALS3.1-HmALS3.4, as the master regulator of this trait. These genes encode primarily tonoplast-localized transporters with a conserved seven-transmembrane structure. Notably, HmALS3.1 is highly conserved with orthologs while HmALS3.2-HmALS3.4 exhibit significant divergence, suggesting functional specialization. We further demonstrate that HmALS3 proteins assemble into oligomeric channels. Crucially, hetero-trimeric complexes exhibit substantially wider pore architectures than homodimers, providing a structural basis for high-capacity Al transport. Functional validation showed that heterologous expression in yeast and Arabidopsis significantly enhanced Al tolerance and accumulation. Conversely, silencing HmALS3 in Hydrangea compromised vacuolar sequestration, triggering a visible blue-to-pink sepal color shift. Comparative genomics further indicates that ALS3 lineage expansion represents a convergent evolutionary strategy among Al-hyperaccumulating species. This expansion enables the assembly of hetero-oligomeric channels with distinct transport properties. Our findings elucidate a sophisticated gene-cluster-based Al-hyperaccumulation mechanism, offering vital genetic targets for engineering Al-tolerant crops and phytoremediation strategies.