Phenotypic and data analysis
After co-cultivation with bacteria for an indicated time period, the length of the newly elongated PR grown during the treatment was quantified and emerged LRs in the whole PR were counted. The plates with seedlings were scanned with EPSON XL11000 for the measurement of PR elongation with Fiji software (http://fiji.sc/) and emerged LRs were recorded under a microscope. The LR density was determined by dividing the LR number by the whole PR length for each seedling analyzed. The total biomass production of each seedling was measured on an analytical balance. LRPs were quantified 6 d after co-cultivation. The pCYCB1:GUS seedlings were stained and cleared to visualize the LRPs at early stages of development and each LRP developmental stages were classified according to Malamy and Benfey (1997) as follows. Stage I, LRP initiation, in the longitudinal plane, approximately 8 to 10 “short” pericycle cells are formed. Stage II, the formed LRP is divided into two layers by a periclinal division. Stage III, the outer layer of the primordium divides periclinally, generating a three-layer primordium. Stage IV, LRP with four cell layers. Stage V-VII, from the LRP is midway through the parent cortex to the LRP appears to be just about to emerge from the parent root.