Increased Cysteine Accumulation is Essential for Salt Stress Tolerance in Arabidopsis Halotolerance 2-Like (AHL)-Overexpressing Transgenic Plants

Cysteine (Cys) regulates plant growth, development, and various abiotic stress responses. However, the knowledge gained from genetic and molecular studies on the role of Cys metabolism in salinity response remains limited. Here, we introduce a sulfate metabolism-related component, Arabidopsis Halotolerance 2-like (AHL), which is involved in salt stress adaptation. AHL expression was experimentally induced under salt stress conditions using AHL promoter-β-glucuronidase transgenic plants. Phenotypic analysis revealed that the survival rate of AHL-overexpressing (AHL-OE) lines was greater than that of wild-type (WT) plants under high-salinity conditions, while ahl mutant and AHL-RNAi seedlings were more sensitive than WT seedlings. Accumulation of Cys and proline was increased in AHL-OE transgenic lines under salinity stress conditions, but malondialdehyde and hydrogen peroxide levels were lower in AHL-OE than in WT, ahl, and AHL-RNAi plants. In addition, the transcription levels of genes associated with Cys biosynthesis and sulfate metabolism were higher in AHL-OE than ahl and AHL-RNAi seedlings after salt stress treatment. Moreover, exogenous application of Cys could rescue the salt stress-induced sensitive phenotypes of ahl and AHL-RNAi lines, and return them to the WT phenotype. Taken together, our findings indicate that AHL positively regulates salinity response in Arabidopsis seedlings by modulating a Cys-dependent pathway.