, Encoding the Small Subunit of Acetolactate Synthase, Is Partially Responsible for Resistance to Hypoxic Stress in .

Flooding is a significant stress to land plants, depriving them of essential oxygen. Plants have evolved diverse strategies with variable success to survive flooding. Similar strategies have been described in organisms from other kingdoms. Several fungal species can successfully survive a low-oxygen environment by increasing their branched-chain amino acid (BCAA) contents. BCAAs may act as alternative electron acceptors in the respiratory chain under an oxygen-limited environment. The key and first enzyme for BCAA biosynthesis is acetolactate synthase (ALS). We identified two homologous genes encoding the small subunit of ALS in Arabidopsis (). We determined that (), which encodes the small subunit of ALS, is strongly expressed in all organs and highly expressed under submergence and low-oxygen stresses. We also showed that the overexpression of confers tolerance to low-oxygen stress. These results indicate that ALS may play an essential role under prolonged flooding or oxygen deficiency in Arabidopsis.