Effect of siaD on Ag-8 to improve resistance to crown gall in grapes and related mechanisms.

Crown gall caused by Agrobacterium vitis (A. vitis) is one of the crucial issues restricting the to grape industry. In this study, Agrobacterium tumefaciens (Ag-8) was separated from the soil that could prevent the occurrence of grape crown gall. By the mutagenesis of Ag-8 transposon, the siaD gene deletion strain (ΔsiaD) showed significantly lower efficacy in grape and tomato plants for controlling grape crown gall, but the relevant mechanism was not clear. The biofilm formation and motility of ΔsiaD were significantly decreased, and the colonization ability of ΔsiaD in tomato roots was significantly reduced. RNA-seq analysis showed that the expression of nemR significantly reduced in the ΔsiaD and that the expression of nemR showed a high correlation with biofilm and motility. Further studies showed that the nemR gene deletion strain of Ag-8 (ΔnemR) showed significantly reduced motility, biofilm formation and control of grape crown gall compared to Ag-8, and the nemR gene complementary strain of Ag-8 (ΔnemR-comp) recovered to Ag-8 wild-type levels. The inoculation experiments of preventive, curative or simultaneous treatment further showed that the preferential inoculation with Ag-8 reduced the incidence of grape crown gall on tomato plants, and studies showed that the mutation of siaD affected the site competition between Ag-8 and A. vitis, and that the mutation of nemR was consistent with the previous results. This study provides a new strategy for the prevention and control of grape crown gall, which is of great significance to the grape industry to increase production and income.