Spatio-temporal orientation of microtubules controls conical cell shape in Arabidopsis thaliana petals

Abstract

The physiological functions of epidermal cells are largely determined by their diverse morphologies. Most flowering plants have special conical-shaped petal epidermal cells that are thought to influence light capture and reflectance, and provide pollinator grips, but the molecular mechanisms controlling conical cell shape remain largely unknown. Here, we developed a live-confocal imaging approach to quantify geometric parameters of conical cells in Arabidopsis thaliana (A. thaliana). Through genetic screens, we identified katanin (KTN1) mutants showing a phenotype of decreased tip sharpening of conical cells. Furthermore, we demonstrated that SPIKE1 and Rho of Plants (ROP) GTPases were required for the final shape formation of conical cells, as KTN1 does. Live-cell imaging showed that wild-type cells exhibited random orientation of cortical microtubule arrays at early developmental stages but displayed a well-ordered circumferential orientation of microtubule arrays at later stages. By contrast, loss of KTN1 prevented random microtubule networks from shifting into well-ordered arrays. We further showed that the filamentous actin cap, which is a typical feature of several plant epidermal cell types including root hairs and leaf trichomes, was not observed in the growth apexes of conical cells during cell development. Moreover, our genetic and pharmacological data suggested that microtubules but not actin are required for conical cell shaping. Together, our results provide a novel imaging approach for studying petal conical cell morphogenesis and suggest that the spatio-temporal organization of microtubule arrays plays crucial roles in controlling conical cell shape.

Barley RIC157 is involved in RACB-mediated susceptibility to powdery mildew

“…2005). The microtubule-severing activity of KTN1 might even be regulated by AtROP2, AtROP4 and AtROP6 (Ren et al . 2017) via AtRIC1.…”

A versatile microfluidic device for highly inclined thin illumination microscopy in the mossPhyscomitrella patens

“…As a proof-of-concept, we imaged microtubule reorganisation associated with regeneration of excised gametophore cells 15 in the microdevice. It is possible that the gametophore excision or injection in the microdevice transiently disrupts the microtubule arrays, based on low anisotropy values ( Figure 3E); however, the anisotropy score was eventually recovered to expected values for cortical microtubules [26][27][28] . Previous study demonstrated that gametophore cells regenerating as protonema produce certain signals, inhibiting protonema regeneration of the surrounding cells 15 .…”

“…Anisotropy score ( Figure 3E) ranging from 0 (purely isotropic arrays) to 1 (purely anisotropic arrays) reflects the alignment of microtubules. For instance, anisotropy values for parallel microtubule arrays, such as cortical microtubules, typically range between 0.2-0.3 [26][27][28] . In our experiments, the initial values for anisotropy were lower than expected (0.09 ± 0.04 at time 0) and recovered in 3 h (0.2 ± 0.11).…”

ROP GTPases Structure-Function and Signaling Pathways

“…Similarly, spk1 and rop2 rop6 rop4RNAi mutants develop cells with wider tip angles. It was proposed that ROP2/6 and ROP4 regulate MTs via KTN1 (Ren et al, 2017). These new findings also suggest that ROP signaling networks play important and general roles in the regulation of cell expansion and cell shape; however, the precise regulatory mechanisms might be distinct in specific organs.…”