(A) Expression pattern of LAX1::GUS in WT leaves one and two. LAX1::GUS was expressed at the tips of developing primordia (arrows in (i), black dashed lines indicate leaf outlines, arrow heads indicate stipules) (a total of 6 plants (with 12 young leaves) were imaged across two separate experiments) and at the tips of serrations (ii) (arrows indicate serrations) (a total of 9 plants (18 leaves) were imaged across three separate experiments). Leaf widths are given above images. (B) Expression pattern of LAX1::GUS in kan1kan2 leaves. LAX1::GUS was expressed at the tips of primordia (i) (a total of 7 plants (14 leaves) were imaged across two separate experiments) and at the tips of outgrowths (ii and iii) (arrows) (20 out of 21 leaves imaged across three separate experiments). ii) shows leaf 1, iii) shows leaf 3. (C) Transverse sections through GUS stained kan1kan2 LAX1::GUS seedlings, showing points of LAX1::GUS expression before outgrowths have emerged (black arrows in i) (data supported by serial sections of 3 other leaves at similar developmental stages in a separate experiment) and at the tips of developing outgrowths (ii) (a total of 8 leaves were imaged across two separate experiments). Dashed orange line in i) indicates leaf outline. (D) AUX1::AUX1:YFP expression in leaf 1 of WT, showing abaxial surface (i) (a total of 15 leaves were imaged across two separate experiments) and adaxial surface (ii) (a total of 4 leaves were imaged in two separate experiments) of two different leaves. (E) AUX1::AUX1:YFP expression in leaf 1 of a kan1kan2 mutant, showing abaxial surface. Arrow points to the tip of an emerging outgrowth with locally elevated AUX1::AUX1:YFP signal (a total of 9 leaves were imaged, across three different experiments). (F) Time-lapse confocal imaging of AUX1::AUX1:YFP in the abaxial epidermis of the first leaf of a kan1kan2 seedling. White arrows mark the positions of cells that eventually gave rise to the AUX1::AUX1:YFP expressing cells in the developing serration on the right side of the leaf. Yellow arrows mark the positions of cells which eventually gave rise to the tip of the ectopic outgrowth on the left side of the leaf. Red and green images in iv), v) and vi) show side views, from the left hand side of the leaf (showing that the outgrowth emerged at the time point shown in v). Red shows auto-fluorescence and a CUC2::RFP marker (used to show the leaf contours), and green shows AUX1::AUX1:YFP signal. Times from the beginning of the experiment at which images were taken are: i) 0 hrs, ii) 22 hr 40 min, iii) 31 hr 10 min, iv) 46 hr 40 min, v) 55 hr 40 min, vi) 74 hr 40 min. Data is consistent with tracking experiments performed for two other kan1kan2 leaves that developed ectopic outgrowths, and with snapshot images of at least 6 leaves before and after outgrowth emergence. (G) Mean number of outgrowths (+/- standard error of the mean) in rosette leaves of kan1kan2 plants carrying mutant alleles of AUX/LAX genes. n numbers are: kan1kan2: 84 leaves from 10 plants, kan1kan2aux1lax1: 110 leaves from 10 plants, kan1kan2aux1lax1lax2: 136 leaves from 10 plants, kan1kan2aux1lax1lax2lax3:200 leaves from 10 plants. (H) Convergent alignment model where elevated intracellular auxin causes elevated rates of auxin import and removal. The model is initialised with elevated auxin degradation at the leaf base (blue cells) and an elevated rate of auxin import and degradation at the leaf tip (blue cells with green outlines). Centres of convergence form within the proximal half of the lamina and when the intracellular auxin concentration exceeds a threshold level, an elevated rate of auxin import and removal is induced (blue cells with green outlines). Scale bars = 50 µm. See Figure 11—figure supplement 1 for LAX2::GUS and LAX3::GUS expression.