Coordinated Regulation of Hypocotyl Cell Elongation by Light and Ethylene through a Microtubule Destabilizing Protein

Abstract

Precise regulation of hypocotyl cell elongation is essential for plant growth and survival. Light suppresses hypocotyl elongation by degrading transcription factor phytochrome-interacting factor 3 (PIF3), whereas the phytohormone ethylene promotes hypocotyl elongation by activating PIF3. However, the underlying mechanisms regarding how these two pathways coordinate downstream effectors to mediate hypocotyl elongation are largely unclear. In this study, we identified the novel MicrotubuleDestabilizing Protein 60 (MDP60), which plays a positive role in hypocotyl cell elongation in Arabidopsis (Arabidopsis thaliana); this effect is mediated through PIF3. Ethylene signaling up-regulates MDP60 expression via PIF3 binding to the MDP60 promoter. MDP60 loss-of-function mutants exhibit much shorter hypocotyls, whereas MDP60 overexpression significantly promotes hypocotyl cell elongation when grown in light compared to the control. MDP60 protein binds to microtubules in vitro and in vivo. The organization of cortical microtubules was significantly disrupted in mdp60 mutant cells and MDP60-overexpressing seedlings. These findings indicate that MDP60 is an important mediator of hypocotyl cell elongation. This study reveals a mechanism in which light and ethylene signaling coordinate MDP60 expression to modulate hypocotyl cell elongation by altering cortical microtubules in Arabidopsis.

Ethylene Signaling Modulates Cortical Microtubule Reassembly in Response to Salt Stress

“…An additional method 196 was used for quantification of the total microtubule length per unit surface area (Fujita 197 et al, 2013 salt stress (Asensi-Fabado et al, 2012;Li et al, 2016). The mutant ein3eil1 is 208 hypersensitive to NaCl treatment (Peng et al, 2014 signaling-inhibited hypocotyl cell elongation in darkness (Sun et al, 2015;Ma et al, 256 2016 Similar to other reports, we found that activation of ethylene signaling greatly alters 374 organization and stability of cortical microtubules in hypocotyl cells (Sun et al, 2015; 375 Ma et al, 2016Ma et al, , 2018. Other phytohormones, such as auxin and brassinosteroid (BR), 376 also affect cortical microtubule organization and stability (Wang et al, 2012;Vineyard 377 et al, 2013).…”

Light‐induced stabilization of ACS contributes to hypocotyl elongation during the dark‐to‐light transition in Arabidopsis seedlings

“…Previous studies have shown that hypocotyl cells of an etiolated seedling are elongated mainly through cell elongation (Smalle et al, 1997;Ma et al, 2018). In particular, the cells beneath the cotyledon-hypocotyl junction covering the apical hook elongate approximately twofold within a day in the dark (Gendreau et al, 1997).…”

Phytochrome Mediates Light Signal for Cortical Microtubule Randomization that Enables Root Hair Formation in Lettuce Seedlings

“…Our finding that phytochrome controls CMT reorganization prior to bulge formation leads to the hypothesis that the increase in Arabidopsis root hair numbers in light (De Simone et al 2000a) could have resulted from enhanced CMT reorganization through phytochrome signaling, similar to the case of lettuce. Realignment of plant's CMT arrays is induced by various environmental and developmental factors including light (Cyr 1994, Le et al 2005, Lian et al 2017, Ma et al 2018. Although there are some reports about the involvement of phytochrome in the reorganization of CMT arrays (Zandomeni and Schopfer 1993, Fischer and Schopfer 1997, Ma et al 2018, these studies were conducted on the aerial parts of the plants.…”

“…Realignment of plant's CMT arrays is induced by various environmental and developmental factors including light (Cyr 1994, Le et al 2005, Lian et al 2017, Ma et al 2018. Although there are some reports about the involvement of phytochrome in the reorganization of CMT arrays (Zandomeni and Schopfer 1993, Fischer and Schopfer 1997, Ma et al 2018, these studies were conducted on the aerial parts of the plants. Our results provide a novel finding which shows involvement of phytochrome in the regulation of CMT arrays in roots.…”

“…The recent study by Ma et al (2018) proposed crosstalk between light-and ethylene-signaling, both of which lead to microtubule reorganization. In this pathway, microtubule organization is altered by its binding with microtubule-destabilizing protein 60 (MDP60), the gene expression of which is regulated by phytochromeinteracting factor 3 (PIF3).…”