Fig. 1: Multiple copies of Mla7 are required to confer resistance to barley powdery mildew caused by Bh.
a–c, Powdery-mildew-susceptible barley cv. SxGP DH-47 was transformed with Mla7 driven by the Mla6 promoter–5′UTR and the Mla6 3′UTR–terminator. Three single-copy insert lines (T1-1, T1-2 and T1-3) and three multiple-copy insert lines (T1-4, T1-8 and T1-12) were identified for Mla7. Resistance to Bh isolates carrying AVRa7 was observed in transgenic barley lines carrying multiple copies of Mla7. Specific recognition of the effector AVRa7 was retained across transgenic lines. Panel a shows infection phenotypes for the presence or absence of transfer DNA (T-DNA) for Mla7 T1 families and controls inoculated with Bh isolate CC148. The presence and absence of T-DNA are shown in orange and blue, respectively. All phenotypes are on a scale from 0 to 4. Transparency and jittering were used to visualize multiple overlapping data points. As shown in b, multiple copies, not single copies, of Mla7 under its native promoter/terminator are required to confer full resistance to Bh isolate CC148. Individual phenotypes from an F2 population with varying numbers of Mla7 transgene copies derived from a cross of two single-insertion transgenic lines (T1-117 and T1-121) are plotted. As shown in c, multicopy lines carrying Mla7 driven by the Mla6 promoter/terminator confers race-specific resistance to barley powdery mildew (Bh). Controls include SxGP DH-47 and near-isogenic lines in the Pallas (Mla8) genetic background: P04B (Mla7) and P06 (Mla7). Bh isolates are ordered according to the presence (AVRa7) or absence (avra7) of the effector recognized by Mla7. Isolates include 3-33 (A), Race I (B), X-4 (C), I-167 (D), K-200 (E), M-236 (F), Z-6 (G), C-132 (H), 120 (I), R86/1 (J), K-3 (K), KM18 (L) and MN-B (M). All experiments were performed twice with similar results; the data shown are the average of these experiments.
