MtCEP1 increases infection and nodulation capacities. A to C, Representative light micrographs of roots 120 h postinoculation (early nodulation stages) with a S. meliloti 1021-GFP strain in the zone of maximal nodulation susceptibility of wild-type (A and B) or ethylene-insensitive skl mutant (C) roots. Curled root hairs are indicated by asterisks. D to F, Green fluorescence images are merged with bright-field pictures shown (A–C), and infection threads penetrating into the cortex are detected in green fluorescence (bars in A–F = 200 μm). G, Quantification of infection pockets, infection threads, and nodules along root segments of equivalent length corresponding to the zone of maximal nodulation susceptibility (n = 12; ANOVA; P < 0.05). Error bars represent se.