Over-expression of a cinnamyl alcohol dehydrogenase-coding gene, GsCAD1, from wild soybean enhances resistance to soybean mosaic virus

Abstract

Abstract Soybean mosaic virus (SMV) is the most prevalent soybean viral disease around the world. As a critical enzyme in secondary metabolism of plants, especially in lignin synthesis, cinnamyl alcohol dehydrogenase (CAD) is widely involved in plant growth and development, and defense pathogen infestation. We performed transcriptome analyses between a high SMV-resistant accession (BYO-15) of wild soybean (Glycine soja) and a SMV-susceptible soybean cultivar (Williams 82) at 7 and 14 days post-inoculation with SMV, found that the expression of GsCAD1 was significantly up-regulated after the inoculation with SMV in the wild soybean, while the GmCAD1 did not show a significant and persistent induction in the soybean cultivar, suggesting GsCAD1 might play a role in SMV resistance. We cloned GsCAD1 and overexpressed it in a SMV-susceptible cultivar Williams 82, we found that two independent GsCAD1-overexpression (OE) lines showed significantly enhanced SMV resistance compared with the non-transformed wild-type (WT) control. Intriguingly, the lignin content in both OE lines were higher than the WT control. Further liquid chromatography (HPLC) analysis showed that the contents of Salicylic Acid (SA) were significantly improved in the OE lines than that of WT, coinciding with the up-regulated expression of an SA synthesis and response gene, PR1. Finally, we observed that either or both replication and intercellular movement of SMV in leaves of the transgenic GsCAD1-OE lines were constrained relative those in non-transgenic WT plants. Collectively, our results suggest that GsCAD1 enhances resistance to SMV in soybean most likely by affecting the contents of lignin and SA.