Abstact

S-type anion channel homologs (SLAH) are widely expressed in various plant tissues and play a key role in anion transport, which is crucial for plant adaptation to both biotic and abiotic stresses. In this study, we employ cryo-electron microscopy (cryo-EM) to analyze four SLAH channel complexes from Arabidopsis thaliana: the homotrimeric SLAH3 channel, the 2SLAH1 + SLAH3+tRNA complex, the 1SLAH1 + 2SLAH3 complex, and the 3SLAH1+tRNA complex. Critically, our studies reveal that tRNA directly binds to and occupies the intracellular entrance of the SLAH1 homotrimer and the 2SLAH1 + SLAH3 heterocomplex. Electrophysiological experiments confirm tRNA's role as a potent inhibitory regulatory subunit: RNase-mediated tRNA degradation robustly activates SLAH1 currents, while targeted mutagenesis of SLAH1 tRNA-interacting residues phenocopy this activation and enhanced ABA-induced stomatal closure. Combining with structural biology, electrophysiology, and biochemistry, we comprehensively examine the key residues in SLAH1 and SLAH3 that are responsible for the anion permeation. This mechanistic advancement provides a deeper understanding of the molecular basis for plant stress tolerance and identifies specific molecular targets for future engineering crops.