Generation of transgenic Arabidopsis

The open reading frame of GeSUT4 cDNA was transferred from pDONR221-f1- GeSUT4 vector to the binary plasmid vector pMDC32 using the LR Gateway technology (Curtis & Grossniklaus 2003). Arabidopsis plants were then transformed with the resulting construct pMDC32-GeSUT4 and four independent homozygous lines were selected as described previously (Guo et al. 2014).Bacillus subtilis colonization assayBacillus subtilis strain 168 harboring a GFP reporter (pAD43-25) (Dunn & Handelsman, 1999) was used for the modified root colonization assays (Allard-Massicotte et al. 2016). In brief, an overnight bacterial culture was inoculated into fresh medium and grown for 3 h to an OD600 of 0.8. Cells were collected and re-suspended at an OD600 of 0.02 in MSNg inoculation medium (4.3 g of MS, 0.05% of glycerol and 10 µg ml-1 of chloramphenicol in 1liter). 7-d-old Arabidopsis seedlings were harvested, washed with sterile water and transferred to a 24-well plate containing 500 µl of the Bacillus solution. After 4 h of incubation, Arabidopsis seedlings were washed with sterilized water and roots were cut off, photographed, and transferred to 1.5 ml Eppondorf tubes containing 1 ml of 0.2% NaCl. Bacillus cells were detached by sonication. Serial dilutions were performed to determine the number of colony-forming unit (CFU) per cm of root.

Statistical analysis

All statistics were performed by Student’s t-test and indicated by one (P< 0.05) or two (P< 0.01) asterisks.