Agrobacterium rhizogenes-mediated transformation of Arachis hypogaea: an efficient tool for functional study of genes

We have developed a technique for efficient transformation of hairy roots of Arachis hypogaea L. using Agrobacterium rhizogenes K599, and have validated this approach for the investigation of gene function. As a model transgene, AhAREB1, a drought-resistance gene from peanut, was fused to green fluorescent protein, and four parameters that might influence the transformation efficiency were tested. The optimal procedure involved the use of petioles with four expanded leaves as explants, infection by K599 at optical density (OD₆₀₀) of 0.6 for 15 min and co-cultivation for 2 d, giving transformation efficiencies of up to 91%. Hairy roots from transgenic peanut plants overexpressing AhAREB1 were unaffected by treatment with polyethylene glycol (PEG), demonstrating increased drought tolerance, whereas control roots showed clear signs of plasmolysis. Transgenic roots accumulated less superoxide anion (O₂ ⁻) than control roots under drought conditions. Additionally, transgenic roots displayed upregulation of four stress-response genes encoding WRKY transcription factor (WRKY33), MYB transcription factor (MYB92), abscisic acid receptor (PYL5) and dehydrin 2 (DHN2).