Wortmannin-induced vacuole fusion enhances amyloplast dynamics in Arabidopsis zigzag1 hypocotyls.
Gravitropism in Arabidopsis shoots depends on the sedimentation of amyloplasts in the endodermis, and a complex interplay between the vacuole and F-actin. Gravity response is inhibited in zigzag-1 (zig-1), a mutant allele of VTI11, which encodes a SNARE protein involved in vacuole fusion. zig-1 seedlings have fragmented vacuoles that fuse after treatment with wortmannin, an inhibitor of phosphatidylinositol 3-kinase, and underscore a role of phosphoinositides in vacuole fusion. Using live-cell imaging with a vertical stage microscope, we determined that young endodermal cells below the apical hook that are smaller than 70 μm in length are the graviperceptive cells in dark-grown hypocotyls. This result was confirmed by local wortmannin application to the top of zig-1 hypocotyls, which enhanced shoot gravitropism in zig-1 mutants. Live-cell imaging of zig-1 hypocotyl endodermal cells indicated that amyloplasts are trapped between juxtaposed vacuoles and their movement is severely restricted. Wortmannin-induced fusion of vacuoles in zig-1 seedlings increased the formation of transvacuolar strands, enhanced amyloplast sedimentation and partially suppressed the agravitropic phenotype of zig-1 seedlings. Hypergravity conditions at 10 g were not sufficient to displace amyloplasts in zig-1, suggesting the existence of a physical tether between the vacuole and amyloplasts. Our results overall suggest that vacuole membrane remodeling may be involved in regulating the association of vacuoles and amyloplasts during graviperception.
Department of Plant and Microbial Biology, North Carolina State University, Raleigh, NC, USA.
Ashley Ann
AA
Alvarez
Department of Plant and Microbial Biology, North Carolina State University, Raleigh, NC, USA.
Sang Won
SW
Han
Japan Science and Technology Agency (JST), Precursory Research for Embryonic Science and Technology (PRESTO), Saitama, Japan.|Department of Botany, University of Wisconsin, Madison, WI, USA.|Department of Biochemistry and Molecular Biology, Saitama University, Saitama, Japan.
Masatsugu
M
Toyota
Department of Plant and Microbial Biology, North Carolina State University, Raleigh, NC, USA.
Carla
C
Brillada
Department of Plant and Microbial Biology, North Carolina State University, Raleigh, NC, USA.
Jiameng
J
Zheng
Department of Botany, University of Wisconsin, Madison, WI, USA.
Simon
0000-0001-9597-6839
S
Gilroy
Department of Plant and Microbial Biology, North Carolina State University, Raleigh, NC, USA mrojasp@ncsu.edu.
Marcela
0000-0003-1051-1827
M
Rojas-Pierce
D000730:Androstadienes / Q000494:pharmacology*; D017360:Arabidopsis / Q000187:drug effects / Q000254:growth & development* / Q000648:ultrastructure; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000502:physiology; D018522:Gravitropism / Q000187:drug effects / Q000502:physiology; D018546:Hypocotyl / Q000187:drug effects / Q000254:growth & development; D008853:Microscopy; D050766:Qb-SNARE Proteins / Q000235:genetics* / Q000502:physiology; D014617:Vacuoles / Q000187:drug effects* / Q000502:physiology / Q000648:ultrastructure; D000077191:Wortmannin
D000730:Androstadienes; D029681:Arabidopsis Proteins; D050766:Qb-SNARE Proteins; C120751:vesicle transport v-SNARE 11 protein, Arabidopsis; D000077191:Wortmannin
Amyloplasts; SNARE; cytoskeleton; gravitropism; vacuole; wortmannin.