Fig. S1 Quantitative and semi-quantitative RT-PCR analyses confirms the down regulation of SGT1, SKP1, RAR1, RBX1 and CUL1c gene transcripts in the silenced plants of Nicotiana benthamiana. Total RNA was extracted from the leaf tissues three weeks post-TRV inoculation and was used to generate first-strand cDNA. RNA from plants inoculated with TRV:GFP was used as a vector control. RT-PCRs were performed with gene specific primers and elongation factor (Ef1α) as the normalizer TRV::GFPTRV::NbSGT1 % mRNA transcripts TRV::GFPTRV::NbSKP TRV::GFPTRV::NbRAR % mRNA transcripts Supporting Information Figs S1-S4 SGT1 RAR1 SKP1 Ef1α Cul1 Wt TRV:GFP TRV:NbCUL1c TRV:NbRBX1 Rbx Ef1α Wt TRV:GFP CUL1c RBX1

TRV::NbSGT1 TRV::GFP TRV::NbSKP1 TRV::NbRAR1 Fig. S2 Effect of SGT1, SKP1 and RAR1 gene silencing on cell division. The effect of gene silencing on cell division was evaluated by placing axenic leaf disks from the gene silenced and TRV:GFP inoculated plants on a non-selective callus inducing medium for 4-weeks and by visualizing the differences in callus production. No difference in calli formation was observed between control and gene silenced plants. Photographs were taken after 4 weeks of callus induction.

TRV::NbSKP1TRV::NbSGT1TRV::00 Fig. S3 Transient expression of GFP by particle bombardment in NbSKP1 and NbSGT1 silenced and empty vector (TRV::00) inoculated leaves of Nicotiana benthamiana. Leaves from the silenced and TRV::00 inoculated plants were transformed using a biolistic method with a plant transformation vector pCAMBIA carrying 35S::GFP cassette. The transformed leaves were observed under fluorescent microscope 48-h after bombardment. No qualitative differences were observed in the number of GFP spots detected in the silenced and TRV::00 inoculated plants.

Col-0 ask1-1 eta3edm1Col0:chvB- ask2-1LerWs Fig. S4 Agrobacterium attachment to cut root ends of mutants and wild-type Arabidopsis. Axenic cut leaf segments derived from edm1, eta3, ask1-1 and ask2-1 mutants and their respective wild-type (Col-0, Ler and Ws) plants were co-cultivated with the disarmed strain A. tumefaciens GV2260 carrying the binary vector pDSK-GFPuv at final concentrations of 1 x 10 8 colony forming units (CFU)/ml or the chvB - attachment deficient strain (5 x 10 8 CFU/ml; right most panel on top line). Twelve hours after co-cultivation, root segments were washed to remove unattached bacteria and the fluorescent bacteria attached to root tissues were visualized along the cut surfaces using a Leica TCS SP2 AOBS confocal system using excitation at 488 nm and emitted light from nm with a 20X dry objective.