Fig. 5: Differential auxin signalling between the two adaxial carpels underlies style deflection in Cyanella alba subsp. flavescens.

A Empirical cumulative distribution functions (ECDFs) of the log2 fold-changes (log2FC) in transcript abundance between carpels 1 and 2 are shown for selected Mercator bins with significantly different log2FC distributions compared to the transcriptome-wide background (‘other bins’). See Supplementary Data 3 for results for all bins. B Log2 fold-changes (log2FC) in transcript abundance between carpels 1 and 2 are shown relative to the average base expression across all samples for all genes in the Mercator bins shown in (A). C, D C. alba flowers from left-biased plants after treatment with lanolin only (C) or lanolin with 5 mg/ml IAA (D) to carpel 2. Grey arrowheads indicate the side where two of the adaxial anthers were removed and lanolin was applied to the carpel 2. Blue arrowheads indicate styles. Dashed lines show the midline of the flower based on the adaxial petal and stamens. One of the three petals in (C) was removed (yellow asterisk). Scale bar is 5 mm. E Effect of auxin on style divergence angle and the ratio of carpel 1 to carpel 2 length (C1/C2 ratio). Positive divergence angles indicate style deflection away from carpel 1, negative angles towards carpel 1. Linear regression lines and R2 values are shown. Both IAA treated samples are significantly different from untreated and lanolin-only samples regarding both C1/C2 ratio and style divergence angle (p < 0.001; t-test). F Schematic model for the development of a consistent floral handedness based on an initial asymmetry in auxin concentration in the initiating organs (gradients in circles, P2 to P0 from old to young; descending indicates the side of the primordium facing the next older primordium) at the shoot meristem (green). The direction of this initial asymmetry depends on the direction of the phyllotactic spiral (curved arrow, counter-clockwise in this illustration) and is later translated into style deflection (to the right in this illustration), by stronger elongation of carpel 1 than carpel 2.