Figure 6.

QSK1 is involved in root development and response to mannitol. A, LR number in wild-type Col-0, qsk1.qsk2 double mutant, qsk1.qsk2 double mutant expressing QSK1-GFP, QSK1-S621D,S626D-GFP, QSK1-S621A,S626A-GFP under 35S promoter. Arabidopsis lines were grown for 9 d on Murashige and Skoog plates for control conditions or 6 d then transferred to MS plate containing 0.4 m mannitol before root phenotyping. LR number is represented by white and red box plots for control and mannitol treatment, respectively. In control conditions, the qsk1.qsk2 double mutant displays a decrease of LR number compared to the wild type. Overexpression of QSK1 and the phosphomimic QSK1-S621D,S626D-GFP reverse this phenotype with more LR. Overexpression of QSK1-S621A,S626A-GFP phosphodead only partially rescues the qsk1.qsk2 double mutant LR number phenotype. In response to mannitol treatment, Col-0 wild-type and Arabidopsis seedlings overexpressing QSK1 and QSK1-S621D,S626D-GFP in the qsk1.qsk2 double mutant background all showed a decrease in LR number, whereas the qsk1.qsk2 double mutant and the qsk1.qsk2 double mutant overexpressing QSK1-S621A,S2626A-GFP display the same number of LR as in control conditions. n = 2 experiments, 10 plants/line/experiments. Two-tailed Wilcoxon statistical analysis, *P < 0.05; **P < 0.01; ***P < 0.001. Scale bars, 10 µm. (B and C) Graphical summary of the gravistimulation and the development stages of the LR primordia (B) adapted from Péret et al. (2012). The LR primordium stages were determined 18 h and 42 h after gravistimulation and are color-coded respectively in black and red (C). At 18 h, the qsk1.qsk2 double mutant display a delay in LR primordium initiation with the absence of LR primordium initiation (stage 0) in 35% of the plants observed. At 42 h, both the qsk1.qsk2 double mutant and QSK1-S621A,S2626A-GFP-expressing lines showed a delay in LR primordium compared to other lines, with no stage VI or VII LR primordium.