Inhibition of isoflavone biosynthesis enhanced T-DNA delivery in soybean by improving plant–Agrobacterium tumefaciens interaction

Abstract

Soybean is a difficult crop to manipulate through Agrobacteriumtumefaciens-mediated genetic transformation. Plant–bacterium interaction plays an important role in the transformation process. Being rich with isoflavones, soybean may have an adverse effect on the A. tumefaciens-mediated genetic transformation. To investigate whether high content of endogenous isoflavones in soybean is a serious obstacle in achieving high efficient Agrobacterium-mediated transformation in soybean, a series of experiments on inhibition of isoflavone biosynthesis were conducted to improve upon soybean transformation efficiency. Results indicated that soybean isoflavones inhibited A. tumefaciens growth and respiration, the transformation efficiency [β-glucuronidase (GUS) transient expression] was negatively correlated with the phenylalanine ammonia-lyase activity and isoflavones content. The biosynthesis of soybean isoflavones was partially inhibited by sonication treatment and applying antagonists in co-culture medium and thereby decreased the adverse effects of isoflavones on Agrobacterium infection. A discernible improvement in transformation efficiency was achieved when sonication at 40 kHz for 3 min was applied along with Agro-infection and the explants were cultured on co-culture medium containing 20 μM α-aminooxyacetic acid (AOA), with the percentage of GUS transient expression as 41.4 %, being 3.6 times higher than that not sonicated and co-cultured on medium without AOA. Sonication was found not only to simply make micro-wounds for Agrobacterium to penetrate or releasing phenolic compounds for induced Agrobacterium vir gene expression; it disturbed the biosynthesis of isoflavones at the transcription level and decreased the adverse effects of isoflavones on soybean transformation, and thereby improving soybean transformation efficiency.