Improvement of soybean transformation via Agrobacterium tumefaciens methods involving α-aminooxyacetic acid and sonication treatments enlightened by gene expression profile analysis.

KEY MESSAGE: Antagonists and sonication treatment relieved the structural barriers of Agrobacterium entering into cells; hindered signal perception and transmission; alleviated defense responses and increased cell susceptibility to Agrobacterium infection. Soybean gene expression analysis was performed to elucidate the general response of soybean plant to Agrobacterium at an early stage of infection. Agrobacterium infection stimulated the PAMPs-triggered immunity (BRI1, BAK1, BZR1, FLS2 and EFR) and effector-triggered immunity (RPM1, RPS2, RPS5, RIN4, and PBS1); up-regulated the transcript factors (WRKY25, WRKY29, MEKK1P, MKK4/5P and MYC2) in MAPK pathway; strengthened the biosynthesis of flavonoid and isoflavonoid in the second metabolism; finally led to a fierce defense response of soybean to Agrobacterium infection and thereby lower transformation efficiency. To overcome it, antagonist α-aminooxyacetic acid (AOA) and sonication treatment along with Agrobacterium infection were applied. This novel method dramatically decreased the expression of genes coding for F3'H, HCT, β-glucosidase and IF7GT, etc., which are important for isoflavone biosynthesis or the interconversion of aglycones and glycon; genes coding for peroxidase, FLS2, PBS1 and transcription factor MYC2, etc., which are important components in plant-pathogen interaction; and genes coding for GPAT and α-L-fucosidase, which are important in polyesters formation in cell membrane and the degradation of fucose-containing glycoproteins and glycolipids on the external surface of cell membrane, respectively. This analysis implied that AOA and sonication treatment not only relieved the structural membrane barriers of Agrobacterium entering into cells, but also hindered the perception of 'invasion' signal on cell membrane and intercellular signal transmission, thus effectively alleviated the defense responses and increased the cell susceptibility to Agrobacterium infection. All these factors benefit the transformation process; other measures should also be further explored to improve soybean transformation.