A SNARE complex containing SGR3/AtVAM3 and ZIG/VTI11 in gravity-sensing cells is important for Arabidopsis shoot gravitropism

Abstract

Plants can sense the direction of gravity and change the growth orientation of their organs. The molecular mechanisms of gravity sensing and signal transduction during gravitropism are not well known. We have isolated several shoot gravitropism (sgr) mutants of Arabidopsis. The sgr3-1 mutant exhibits a reduced gravitropic response in the inflorescence stems. In the inflorescence stems of Arabidopsis, gravity is sensed in endodermal cells that contain sedimentable amyloplasts. In sgr3-1, some amyloplasts in the endodermis failed to sediment in the direction of gravity. SGR3 encodes a syntaxin, AtVAM3, which had previously been cloned as a homologue of yeast Vam3p. AtVAM3 is localized to the prevacuolar compartment and vacuole and is suggested to function in vesicle transport to the vacuole. We have also cloned another soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE), ZIG͞AtVTI11, a mutation that causes abnormal gravitropism. This mutant displayed an abnormal distribution of amyloplasts in the endodermal cells similar to that in sgr3-1. Endodermis-specific expression of SGR3 and ZIG by using the SCR promoter could complement the abnormal shoot gravitropism of each mutant. Protein-protein interaction between AtVAM3 and AtVTI11 in the endodermal cells was detected immunologically. The sgr3-1 mutation appeared to reduce the affinity of AtVAM3 for AtVTI11 or SYP5. These results suggest that vesicle transport to the prevacuolar compartment͞vacuole in the endodermal cells, mediated by a specific SNARE complex containing AtVAM3 and AtVTI11, plays an important role in shoot gravitropism.

Overexpression of theArabidopsisSyntaxin PEP12/SYP21 Inhibits Transport from the Prevacuolar Compartment to the Lytic Vacuole in Vivo

“…SYP22 was both localized to the tonoplast and the PVC in Arabidopsis (Sato et al, 1997;. A complex between SYP22, VTI11, and SYP51 has been suggested to operate at the tonoplast and may control PVC-to-vacuole traffic (Surpin et al, 2003;Yano et al, 2003).…”

MODIFIED VACUOLE PHENOTYPE1 Is an Arabidopsis Myrosinase-Associated Protein Involved in Endomembrane Protein Trafficking

“…Protein trafficking through the endomembrane system requires specific cargo recognition and delivery mechanisms that are mediated by a series of highly specific targeting signals (Surpin and Raikhel, 2004), whose proper recognition is critical for the function of numerous downstream processes, such as floral development (Sohn et al, 2007), gravitropism (Kato et al, 2002;Surpin et al, 2003;Yano et al, 2003), abiotic stress tolerance (Zhu et al, 2002), autophagy (Surpin et al, 2003;Bassham., 2007), pathogen defense (Robatzek, 2007), and turgor pressure and growth (De, 2000).…”

Analyses of a Gravistimulation-Specific Ca2+ Signature in Arabidopsis using Parabolic Flights

“…The most often referred to hypothesis of gravisensing is the starch-statolith hypothesis (Kiss, 2000;Morita, 2010); Perbal and Driss-Ecole (2003) proposed that sedimentation of the high-density plastids, amyloplasts, causes membrane stretch (or stress in the network of actin filaments), leading to the activation of mechanically sensitive channels in the plant plasma membrane. Analysis of shoot gravitropism (sgr) mutants (e.g., sgr2, zigzag [zig]/ sgr4, or sgr9) has shown that their abnormal shoot gravitropism can be explained by the abnormalities in the amyloplast sedimentation Morita et al, 2002;Yano et al, 2003;Nakamura et al, 2011). The amyloplast sedimentation after changing the gravity vector was directly observed with a vertical-stage fluorescence microscope (Saito et al, 2005;Nakamura et al, 2011), which showed that movement of the amyloplast sedimentation takes several minutes.…”