AM initiation requires <i>STM</i>-expressing cells.

<p>(A) Schematic representation of axillary bud formation in leaf axils of Col-0 wild-type plants and the <i>stm-bum1</i> mutant plants. The thick black horizontal line represents the border between the youngest rosette leaf and the oldest cauline leaf. For Col-0, each column represents a single plant, and each square within a column represents an individual leaf axil. For <i>stm-bum1</i>, each column represents a single main branch, and branches from a single plant are grouped together. The bottom row represents the oldest rosette leaf axils, with progressively younger leaves above. Green indicates the presence of an axillary bud, yellow indicates the absence of an axillary bud, red indicates the presence of a single leaf in place of an axillary bud, and orange indicates the presence of a terminated axillary bud in any particular leaf axil. (B, C, E and F) Leaf axils (as shown in <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1006168#pgen.1006168.g001" target="_blank">Fig 1B</a>) showing cells with STM-Venus (green) expression before laser ablation (B and E) and after laser ablation (C and F). The regions bordered by the white dotted line (in C and F) are subject to laser ablation. (D and G) Axillary bud formation 12 d after laser ablation, as shown in (C and F). Arrows show presence (D) and absence (G) of an axillary bud. Note axillary buds formed only when <i>STM</i>-expressing cells remain intact (B-D). Arrowheads highlight the approximate center of the incision lines. Bars = 50 μm in (B, C, E, and F) and 1 mm in (D and G).