Fig. 2.

Wild-type S. meliloti 1021 (a–d) and the exoY mutant (e–f) are trapped in CCRHs of M. truncatula at 3 dpi but have not yet initiated infection threads. M. truncatula roots at 3 dpi with GFP-expressing S. meliloti wild type (a–d) or exoY mutant (e–f). (a, c, and e) Brightfield images. (b, d, and f) Brightfield/GFP-fluorescence overlays. (Scale bars: 20 μm.) [In M. truncatula inoculated with strain ABS7 of S. meliloti, infection threads have been observed penetrating the root epidermis at 3 dpi (21, 49). However, for S. meliloti 1021 under our conditions, at 3 dpi, infection threads have not yet initiated.]