Fig. 4.

Sucrose is the host signal that induces sghA expression. (A) X-gal plate assay of strain A6 sghA-encoded β-galactosidase activity in the presence or absence of carrot extract. A6, wild-type A. tumefaciens A6; sghRA::Tn, negative control of A. tumefaciens A6 with mutations in SghA and SghR. (B) Sucrose induced the expression of sghA in A6 on solid plates containing X-gal where A. tumefaciens A6 was spotted as the indictor strain on separated agar slices. The solid arrow in A and B represents the loading location of carrot extract and related compounds (5 µL of solution with a concentration of 1 M) on separated BM agar slices. The dashed arrow indicates the diffusion direction of the compounds. (C) EMSA analysis of sucrose activity in dissociation of SghR-promoter (PsghA) complex. Experiments were repeated at least 3 times with similar results, and 1 set of representative data is presented.