Characterization of Al3+-toxicity responses and molecular mechanisms underlying organic acid efflux in Vigna mungo (L.) Hepper.

Aluminium (Al³⁺) toxicity in acidic soils poses a significant challenge for crop cultivation and reduces crop productivity. The primary defense mechanism against Al³⁺ toxicity involves the activation of organic acid secretion. In this study, responses of 9 Vigna mungo cultivars to Al³⁺ toxicity were investigated, with a particular emphasis on the root system and crucial genes involved in Al³⁺ tolerance using molecular cloning and expression analysis. Sensitive blackgram-KM2 cultivars exposed to 100-µM Al³⁺ toxicity for 72 h exhibited a root-growth inhibition of approximately 66.17%. Significant loss of membrane integrity and structural deformative roots were found to be the primary symptoms of Al³⁺ toxicity in blackgram. MATE (Multidrug and Toxic Compound Extrusion) and ALS3 (Aluminium Sensitive 3) genes were successfully cloned from a sensitive blackgram cv KM2 with phylogenetic analysis revealing their evolutionary relationship to Vigna radiata and Glycine max. The MATE gene is mainly localized in the plasma membrane, and highly expressed under Al³⁺, thus suggesting its role in transports of citrate-Al³⁺ complexes, and detoxifying Al³⁺ within plant cells. In addition, ALS3 was also induced under Al³⁺ toxicity, which codes the UDP-glucose transporter and is required for the maintenance of ions homeostasis. In summary, this study highlights the understanding of Al³⁺ toxicity and underlying molecular mechanisms linked to the efflux of organic acid in blackgram, ultimately aiding the framework for the development of strategies to enhance the resilience of blackgram and other pulse crops in Al-rich soils.