Fig 1.
SL and KL signalling additively regulate lateral root density.
(A) Primary root length (experiment 3 in S1 Fig) and (B) lateral root density (experiment 1 in S1 Fig) of Col-0 wild type, the strigolactone perception mutant d14-1 and the strigolactone biosynthesis mutants max3-9, max4-5 and max1-1 (arranged in pathway order). (C) Primary root length and (D) lateral root density in the d14-1 kai2-2 double mutant and the respective single mutants. Data in (C) form part of the same dataset in (A), and PRL for the Col-0 and d14-1 genotypes are also shown in (A). LRD was recorded at 10 dpg. The outline of the violin plots represents the probability of the kernel density. Black boxes represent interquartile ranges (IQR), with the red horizontal line representing the median; whiskers extend to the highest and lowest data point but no more than ±1.5 times the IQR from the box; outliers are plotted individually. Different letters indicate different statistical groups (ANOVA, posthoc Tukey, p≤ 0.001 (A) F4,111 = 11.81, n = 19–25 (B) F4,58 = 5.626, n = 8–18 (C) F3,88 = 17,83, n = 21–26 (D) F3,63 = 19.82, n = 11–18).
Fig 2.
KL perception mutants are impaired in root hair development.
(A) Diagram showing the primary root zone used for root hair phenotyping (curly bracket). Root hair density and length were quantified in 1 mm primary root length between 2 and 3 mm from the root tip. (B) Representative images of root hair phenotypes of the indicated genotypes. Scale bar, 1 mm. (C,E,G) Root hair density and (D,F,G) root hair length in (C,D) Col-0 wild type, the strigolactone perception mutant d14-1 and the strigolactone biosynthesis mutants max3-9, max4-5 and max1-1 (arranged in pathway order), (E,F) the indicated karrikin perception mutants and (G,H) Ler wild type and indicated karrikin perception mutants, treated with solvent (70% Methanol) or 1 μM KAR2.. The outline of the violin plots represents the probability of the kernel density. Black boxes represent interquartile ranges (IQR), with the red horizontal line representing the median; whiskers extend to the highest and lowest data point but no more than ±1.5 times the IQR from the box; outliers are plotted individually. Different letters indicate different statistical groups (ANOVA, posthoc Tukey, (C) F4,65 = 0.242, n = 10–18; p≤0.05, (D) F4,718 = 1.291, n = 10–13, p≤0.05, (E) F4,88 = 28.9, n = 11–24, p≤0.001), (F) F4,825 = 23.43, n = 10–13, p≤ 0.001, (G) F7,96 = 60.79, n = 10–15, p≤ 0.001, (H) F7,975 = 45.39, n = 10–13, p≤ 0.001).
Fig 3.
KL perception mutants display exaggerated skewing and waving.
(A) Diagram showing how skewing-angle and root straightness were determined. Skewing was quantified by measuring the angle between the vertical axis (Ly) defined as 0°, and the root tip. Right or left skewing is indicated by positive or negative values, respectively. Straightness was calculated as the ratio of the straight line between the hypocotyl-root junction and the root tip (green line, Lc) and the total root length (L). (B) Images of representative 5-days-old seedlings of the indicated genotypes. Scale bars, 1 mm. (C, D) Root skewing and (E and F) root straightness of the indicated genotypes. The outline of the violin plot represents the probability of the kernel density. Black boxes represent interquartile ranges (IQR), the red horizontal line representing the median; whiskers extend to the highest and lowest data point but no more than ±1.5 times the IQR from the box; outliers are plotted individually. Different letters indicate different statistical groups (ANOVA, posthoc Tukey, p≤ 0.001, (C) F3,315 = 16.08, n > 60 (D) F4,347 = 4.762, n > 50 (E) F3,315 = 13.62, n > 60 (F) F4,347 = 4.28, n > 50).
Fig 4.
KL perception mutants exhibit decreased epidermal cell lengths and root diameter.
(A) Number of root epidermal cells per mm of the indicated genotypes. (B) Images of representative roots between 2 and 3 mm from the root tip of 5-days-old seedlings of the indicated genotypes. Scale bars, 0.1 mm. (C) Root cell length and (D) root diameter of the indicated genotypes. The outline of the violin plots represents the probability of the kernel density. Black boxes represent interquartile ranges (IQR), the red horizontal line representing the median; whiskers extend to the highest and lowest data point but no more than ±1.5 times the IQR from the box; outliers are plotted individually. Different letters indicate different statistical groups (ANOVA, posthoc Tukey, (A) F4,52 = 4.715, n = 9–13, p≤ 0.01, (C) F3,392 = 10.64, n = 10–11, p≤ 0.001, (D) F4,50 = 15.95, n = 10–12, p≤0.001).
Fig 5.
SMAX1 and SMXL2 regulate skewing and root straightness.
(A, B, E, F) Root skewing and (C, D, G) root straightness in Col-0 wild type and the indicated genotypes (the mutant alleles are max2-1, smax1-2, smxl2-1, smxl6-4, smxl7-3 and smxl8-1). The outline of the violin plot represents the probability of the kernel density. Black boxes represent interquartile ranges (IQR), with the red horizontal line representing the median; whiskers extend to the highest and lowest data point but no more than ±1.5 times the IQR from the box; outliers are plotted individually. Different letters indicate different statistical groups (ANOVA, posthoc Tukey, p≤0.001 (A) F3,345 = 7.612, n > 60; (B) F5,259 = 5.051, n > 30; (C) F3,440 = 16.32, n > 60; (D) F5,261 = 6.57, n > 30 (E) F3,209 = 8.784, n > 45 (F) F3,209 = 10.22, n > 45; (G) F5,127 = 21.07, n = 21). [M] = experiment performed in Munich, [L] = experiment performed in Leeds.
Fig 6.
Lateral root density is regulated by both SMAX1/SMXL2 and SMXL678.
Lateral root density in Col-0 wild type and the indicated genotypes (the mutant alleles are max2-1, smax1-2, smxl2-1, smxl6-4, smxl7-3 and smxl8-1). The outline of the violin plots represents the probability of the kernel density. Black boxes represent interquartile ranges (IQR), with the red horizontal line representing the median; whiskers extend to the highest and lowest data point but no more than ±1.5 times the IQR from the box; outliers are plotted individually. Asterisks indicate a significant difference with wild type (ANOVA, posthoc Dunnett´s test comparing to wild-type, F5,90 = 10.62, n = 10–17; *p ≤ 0 .05, **p ≤ 0.01, ***p ≤ 0.001).
Fig 7.
SMAX1 and SMXL2 regulate root hair development.
(A, C, E) Root hair density and (B, D, F) root hair length in Col-0 wild type and the indicated genotypes (the mutant alleles are max2-1, smax1-2, smxl2-1, smxl6-4, smxl7-3 and smxl8-1). The outline of the violin plot represents the probability of the kernel density. Black boxes represent interquartile ranges (IQR), with the red horizontal line representing the median; whiskers extend to the highest and lowest data point but no more than ±1.5 times the IQR from the box; outliers are plotted individually. Different letters indicate different statistical groups (ANOVA, posthoc Tukey, p≤ 0.001 (A) F17,385 = 79.17, n = 9–13 (B) F3,44 = 67.45, n = 9–11 (C) F3,39 = 20.33, n = 9–11 (D) F3,615 = 30.02, n = 9–11 (E) F3,44 = 67.45, n = 9–15 (F) F3,410 = 38.66, n = 8–11).
Fig 8.
The two GR24 stereoisomers regulate root hair development through both D14 and KAI2.
(A) Root hair density and (B) root hair length of the indicated genotypes treated with solvent (acetone), 1 μM μM GR24ent-5DS, 1 μM GR245DS or 1 μM rac-GR24. The outline of the violin plot represents the probability of the kernel density. Black boxes represent interquartile ranges (IQR), with the red horizontal line representing the median; whiskers extend to the highest and lowest data point but no more than ±1.5 times the IQR from the box; outliers are plotted individually. Different letters indicate different statistical groups (ANOVA, posthoc Tukey, n = 8–11 (A) F19,3740 = 1.983; p≤ 0.01 (B) F19,3740 = 57.83, p≤ 0.001).
Fig 9.
Model for KL and SL signalling regulating Arabidopsis root development.
SL and KL signalling act through the proteasomal degradation of SMXLs in Arabidopsis roots. As in the shoot [30] SMAX1 and SMXL2 are targets of KL perception, while SMXL6,7,8 are targets of SL perception. SMAX1 represses root diameter. SMAX1 and SMXL2 repress root hair development and promote root skewing and root straightness. SMAX1, SMXL2, and SMXL6,7,8 promote lateral root development and probably repress cell elongation. Relationships, which are inferred from circumstantial evidence (or for KL signalling from SL signalling) are shown by a dashed arrow or frame.