Overexpression of a Cinnamyl Alcohol Dehydrogenase-Coding Gene, GsCAD1 , from Wild Soybean Enhances Resistance to Soybean Mosaic Virus.

Soybean mosaic virus (SMV) is the most prevalent soybean viral disease in the world. As a critical enzyme in the secondary metabolism of plants, especially in lignin synthesis, cinnamyl alcohol dehydrogenase (CAD) is widely involved in plant growth and development, and in defense against pathogen infestation. Here, we performed RNAseq-based transcriptome analyses of a highly SMV-resistant accession (BYO-15) of wild soybean () and a SMV-susceptible soybean cultivar (Williams 82), also sequenced together with a resistant plant and a susceptible plant of their hybrid descendants at the F3 generation at 7 and 14 days post-inoculation with SMV. We found that the expression of (from ) was significantly up-regulated in the wild soybean and the resistant F3 plant, while the from the cultivated soybean () did not show a significant and persistent induction in the soybean cultivar and the susceptible F3 plant, suggesting that might play an important role in SMV resistance. We cloned and overexpressed it in the SMV-susceptible cultivar Williams 82, and we found that two independent -overexpression (OE) lines showed significantly enhanced SMV resistance compared with the non-transformed wild-type (WT) control. Intriguingly, the lignin contents 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 more improved in the OE lines than that of the wild-type (WT), coinciding with the up-regulated expression of an SA marker gene. Finally, we observed that -overexpression affected the accumulation of SMV in leaves. Collectively, our results suggest that enhances resistance to SMV in soybeans, most likely by affecting the contents of lignin and SA.