Evidence for altered polar and lateral auxin transport in the gravity persistent signal (gps) mutants of Arabidopsis

Abstract

Plant shoots do not respond when they are reoriented relative to gravity at 4 °°°° C. However, when returned to vertical at room temperature, these organs bend in response to the previous cold gravistimulation. The inflorescence stem of the Arabidopsis thaliana gravity persistent signal (gps) mutants respond abnormally after the cold gravistimulation: gps 1 does not bend when returned to room temperature, gps 2 bends the wrong way and gps 3 over-responds, curving past the predicted angle. In wild type and the mutants, basipetal auxin transport in the inflorescence stem was abolished at 4 °°°° C but restored when plants were returned to room temperature. In gps 1, auxin transport was increased; in both gps 2 and gps 3, no significant difference was found when compared to wild type. Expression of the auxin-inducible P IAA2 ::GUS reporter gene, indicated that auxin-induced gene expression was redistributed to the lower side of the inflorescence stem in wild type after gravistimulation at 4 °°°° C. In gps 1, no asymmetries in P IAA2 ::GUS expression were seen. In gps 2, P IAA2 ::GUS expression was localized to the upper side of the stem and in gps 3, asymmetric P IAA2 ::GUS expression was extended throughout the elongation zone of the inflorescence stem. These results are consistent with altered lateral Indole-3-acetic-acid (IAA) gradients being responsible for the phenotype of each mutant.

Auxin Response inArabidopsisunder Cold Stress: Underlying Molecular Mechanisms

“…However, comparatively little insight has been gained so far about the response of this hormone under temperature stress. Previous studies have shown that high temperature alters the plant's auxin response by altering its biosynthesis , whereas cold temperature affects the polar and lateral transport of auxin (Morris, 1979;Wyatt et al, 2002;Nadella et al, 2006). Although these studies demonstrate a link between auxin and temperature stress, the molecular and cellular mechanisms that regulate the auxin response under temperature stress, particularly for cold, remain elusive.…”

“…This demonstrates the existence of a gravity-persistent signal and indicates that cold stress acts after gravity perception (Fukaki et al, 1996;Wyatt et al, 2002). Furthermore, basipetal auxin transport in the inflorescence was abolished at 48C but was restored to the wild-type level soon after the plant was returned to room temperature (Wyatt et al, 2002;Nadella et al, 2006). To identify components that separate the perception events from the response, Wyatt et al (2002) screened for mutants in which the gravity-persistent signal was aberrant.…”

“…Although these gps mutants respond abnormally to the gravity stimulus, the amyloplast sedimentation is apparently normal, suggesting that the aberrant response is caused by an event (or events) that links gravity perception to auxin transport (Wyatt et al, 2002). Additional studies of gps mutants revealed that these mutants fail to establish the proper auxin gradient in the inflorescence after gravistimulation and also show altered polar and lateral auxin transport (Nadella et al, 2006). In an earlier report, Morris (1979) demonstrated that temperature affects the velocity of exogenous auxin transport in a number of species.…”

Auxin Immunolocalization Implicates Vesicular Neurotransmitter-Like Mode of Polar Auxin Transport in Root Apices

“…4,29 Other puzzling data also fall in the right place. For instance, the rapid blockage of PAT after cold exposure, 56,57 which is also known to block endocytosis in root cells, 16 and almost immediate recovery of PAT after returning the plants to room temperature. 56,57 For example, the finding that synaptic proteins occur in plants, like the Arabidopsis protein BIG which is present in plant and animal genomes.…”

“…For instance, the rapid blockage of PAT after cold exposure, 56,57 which is also known to block endocytosis in root cells, 16 and almost immediate recovery of PAT after returning the plants to room temperature. 56,57 For example, the finding that synaptic proteins occur in plants, like the Arabidopsis protein BIG which is present in plant and animal genomes. This protein, which has similarity to the synaptic protein CALLOSIN/ PUSHOVER driving synaptic signal transmission at neuromuscular synapses, is essential for PAT in plants 12,58 and its action is related to endocytosis and vesicle recycling at plant end-poles acting as plant synapses.…”