Disease relevance of Gravitropism

• The response to auxin of rapeseed (Brassica napus L.) roots displaying reduced gravitropism due to transformation by Agrobacterium rhizogenes [1].

High impact information on Gravitropism

• Arabidopsis AUX1 gene: a permease-like regulator of root gravitropism [2].
• The plant hormone auxin regulates various developmental processes including root formation, vascular development, and gravitropism [2].
• Expression studies using an auxin-regulated reporter suggest that AUX1 is necessary for root gravitropism by facilitating basipetal auxin transport to distal elongation zone tissues [3].
• EIR1, a root-specific protein involved in auxin transport, is required for gravitropism in Arabidopsis thaliana [4].
• Intracellular trafficking and proteolysis of the Arabidopsis auxin-efflux facilitator PIN2 are involved in root gravitropism [5].

Biological context of Gravitropism

• By contrast, gravitropism and auxin-induced gene expression in the root, which were promoted by functionally redundant NPH4/ARF7 and ARF19 proteins, were inhibited by shy2-2, but not by bdl protein [6].
• We have isolated a dominant, auxin-insensitive mutant of Arabidopsis thaliana, massugu2 (msg2), that displays neither hypocotyl gravitropism nor phototropism, fails to maintain an apical hook as an etiolated seedling, and is defective in lateral root formation [7].
• ARL2 is expressed at low levels in all organs of seedlings and plants. arl2-1 arg1-2 double mutant roots display kinetics of gravitropism similar to those of single mutants [8].
• We report our studies on root gravitropism indicating that reactive oxygen species (ROS) may function as a downstream component in auxin-mediated signal transduction [9].
• Recently, protein phosphorylation and dephosphorylation mediated by protein kinases and phosphatases, respectively, have been implicated in regulating polar auxin transport and root gravitropism [10].

Anatomical context of Gravitropism

• These results suggest that vesicle transport to the prevacuolar compartment/vacuole in the endodermal cells, mediated by a specific SNARE complex containing AtVAM3 and AtVTI11, plays an important role in shoot gravitropism [11].
• The actin cytoskeleton has been implicated in regulating plant gravitropism [12].
• We conclude that the 45Ca2+ fed to pea epicotyls occurs largely in the cell wall, and that auxin movement is primary and Ca2+ movement secondary in gravitropism [13].
• As an implication we infer that an intact near-UV/blue-light photoreceptor system is required even in darkness for negative gravitropism, the ethylene response and autochemotropism [14].
• The microtubule cytoskeleton does not integrate auxin transport and gravitropism in maize roots [15].

Associations of Gravitropism with chemical compounds

• Rapid redistribution of auxin-regulated RNAs during gravitropism [16].
• Constitutive overexpression of ROP2 results in enhanced polar accumulation of PIN2 protein in the root elongation region and increased gravitropism, which is significantly affected by latrunculin B, an inhibitor of F-actin assembly [17].
• The tt4(2YY6) roots had delayed gravitropism that was chemically complemented with a flavonoid intermediate [18].
• Here we show that mutations in the Arabidopsis thaliana AGRAVITROPIC 1 (AGR1) gene involved in root gravitropism confer increased root-growth sensitivity to auxin and decreased sensitivity to ethylene and an auxin transport inhibitor, and cause retention of exogenously added auxin in root tip cells [19].
• We have also cloned another soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE), ZIG/AtVTI11, a mutation that causes abnormal gravitropism [11].

Gene context of Gravitropism

• SGR2, a phospholipase-like protein, and ZIG/SGR4, a SNARE, are involved in the shoot gravitropism of Arabidopsis [20].
• ARG1 (ALTERED RESPONSE TO GRAVITY) is required for normal root and hypocotyl gravitropism [21].
• The zig-1 mutant of Arabidopsis lacking Qb-SNARE VTI11 shows little shoot gravitropism and abnormal stem morphology [22].
• On the other hand, seedlings with a null mutation in ARL1, a paralog of ARG1 and ARL2, behave similarly to the wild type in gravitropism and other related assays [8].
• Taken together, these results suggest that EGY1 metalloprotease is required for chloroplast development and, hence, a defective EGY1 gene has pleiotropic effects both on chloroplast development and on ethylene-dependent gravitropism of light-grown hypocotyls [23].

Analytical, diagnostic and therapeutic context of Gravitropism

• Differential auxin transport from the columella to lateral root cap cells as a result of root gravitropism has recently been shown using a GFP-based auxin biosensor [24].
• Subsequent perfusion of EGTA-treated plants with calcium completely restores gravitropism; post-perfusion with water does not [25].

References