Abstract
Strigolactones are plant hormones regulating cytoskeleton-mediated developmental events in roots, such as lateral root formation and elongation of root hairs and hypocotyls. The latter process was addressed herein by the exogenous application of a synthetic strigolactone, GR24, and an inhibitor of strigolactone biosynthesis, TIS108, on hypocotyls of wild-type Arabidopsis and a strigolactone signaling mutant max2-1 (more axillary growth 2-1). Owing to the interdependence between light and strigolactone signaling, the present work was extended to seedlings grown under a standard light/dark regime, or under continuous darkness. Given the essential role of the cortical microtubules in cell elongation, their organization and dynamics were characterized under the conditions of altered strigolactone signaling using fluorescence microscopy methods with different spatiotemporal capacities, such as confocal laser scanning microscopy (CLSM) and structured illumination microscopy (SIM). It was found that GR24-dependent inhibition of hypocotyl elongation correlated with changes in cortical microtubule organization and dynamics, observed in living wild-type and max2-1 seedlings stably expressing genetically encoded fluorescent molecular markers for microtubules. Quantitative assessment of microscopic datasets revealed that chemical and/or genetic manipulation of strigolactone signaling affected microtubule remodeling, especially under light conditions. The application of GR24 in dark conditions partially alleviated cytoskeletal rearrangement, suggesting a new mechanistic connection between cytoskeletal behavior and the light-dependence of strigolactone signaling.
Highlights
Following germination in the soil, the developing seedling grows in a manner defined by the surrounding physical conditions
Our results suggest that GR24 affects plant microtubule organization and dynamics under light and that this can be alleviated by etiolation
Under the light/dark regime, GR24 was applied at two different concentrations (3 μM and 25 μM), stalled hypocotyl elongation (Figure 1)
Summary
Following germination in the soil, the developing seedling grows in a manner defined by the surrounding physical conditions Growth patterns, in this case, are related to the underground quality of light (Sheerin and Hiltbrunner, 2017; Yu and Huang, 2017), the mechanical impedance of the soil (e.g., Zhong et al, 2014; Yao et al, 2017), gravity (Zhu et al, 2019), and other factors. Such physical stimuli are integrated into whole plant responses of both the root and the aerial parts of the seedling by production, transport, and differential action of various plant hormones. These hormones, including ethylene, auxin, cytokinin, and others, may have opposing or additive roles during the early stages of seedling growth. Auxin promotes hypocotyl elongation in light conditions, but has rudimentary effects in the dark (Jensen et al, 1998), while cytokinins establish an acropetal root gradient underlying the developmental zonation of the root (Montesinos et al, 2020)
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