CFP and infection: To better define how VPY contributes to infection thread development in root hairs, we used live cell imaging to compare the earliest stages of root hair infection in the M. truncatula vpy-1 mutant and in sunn-2 plants after inoculation with the GFP-tagged Sinorhizobium meliloti strain Sm2011 (Sm2011-CFP) (Fig. 1a–h).