The pARF5::ARF5-GUS line occasionally showed a pale GUS signal only in cells at the edge of the syncytia (Figure 4C; Supplementary Figure 3), but no clear signal within the syncytia at any of the infection stages analyzed (1, 3, 7, and 13 dpi; Figures 4B–E), although it showed the expected activation pattern in uninfected roots (Figure 4A). The gene discussed is ARF5; the disease is infection.