Fig. 6: Disruption of GTRC reversed the gravity-triggered asymmetric distribution of actin filaments.

a Three-week dark-grown WT protonemata showed negative gravitropism and gtrC-16 protonemata showed positive gravitropism after gravistimulation for 2 weeks on vertically orientated culture plate. b Kinetic curved angles of WT and gtrC-16 filaments under gravistimulation (means ± s.d., n ≥ 18). Source data are provided as a Source Data file. c The apical cells of Lifeact-mCherry protonemata growing upwards under gravistimulation. Actin tended to accumulate at the upper part of tip region (white arrowheads). d The apical cells of Lifeact-mCherry/gtrC protonemata growing downwards under gravistimulation. Actin tended to accumulate at the lower part of tip region (white arrowheads). In (c, d), protonemata expressing Lifeact-mCherry were grown in the dark vertically for 1 week and then turned 90 degrees to be gravistimulated. Three representative tip cells were shown for each genotype, and the mCherry signals at two time points were merged to show cell elongation. Magenta and white represent earlier and later time points respectively, with an interval of around half an hour. Yellow lines depict the contour of tip cells at earlier time points. For each genotype, the fluorescence of 10 cells was collected. Arrows labeled with “g” indicate the direction of gravity vectors. Scale bars, 10 μm. e The model of the roles of GTRC in gravitropism. In WT protonemata, after gravistimulation, motor GTRC transfers unknown cargoes to the minus end of microtubules, resulting in the accumulation of actin filaments at the upper region of apical cell, which triggers negative gravitropism. In gtrC protonemata, deficiency of GTRC leads to abnormal cargo distribution, resulting in accumulation of actin filaments at the lower region of apical cell, which triggers positive gravitropism.