Cortical Microtubule Arrays Are Initiated from a Nonrandom Prepattern Driven by Atypical Microtubule Initiation    

Abstract

The ordered arrangement of cortical microtubules in growing plant cells is essential for anisotropic cell expansion and, hence, for plant morphogenesis. These arrays are dismantled when the microtubule cytoskeleton is rearranged during mitosis and reassembled following completion of cytokinesis. The reassembly of the cortical array has often been considered as initiating from a state of randomness, from which order arises at least partly through self-organizing mechanisms. However, some studies have shown evidence for ordering at early stages of array assembly. To investigate how cortical arrays are initiated in higher plant cells, we performed live-cell imaging studies of cortical array assembly in tobacco (Nicotiana tabacum) Bright Yellow-2 cells after cytokinesis and drug-induced disassembly. We found that cortical arrays in both cases did not initiate randomly but with a significant overrepresentation of microtubules at diagonal angles with respect to the cell axis, which coincides with the predominant orientation of the microtubules before their disappearance from the cell cortex in preprophase. In Arabidopsis (Arabidopsis thaliana) root cells, recovery from drug-induced disassembly was also nonrandom and correlated with the organization of the previous array, although no diagonal bias was observed in these cells. Surprisingly, during initiation, only about one-half of the new microtubules were nucleated from locations marked by green fluorescent protein-g-tubulin complex protein2-tagged g-nucleation complexes (g-tubulin ring complex), therefore indicating that a large proportion of early polymers was initiated by a noncanonical mechanism not involving g-tubulin ring complex. Simulation studies indicate that the high rate of noncanonical initiation of new microtubules has the potential to accelerate the rate of array repopulation.

How selective severing by katanin promotes order in the plant cortical microtubule array

“…The same interaction function is also used by other researchers, with varying values for Pcat (14,15). These basic dynamic parameters are the same as in our previous simulation studies (16,33,34). We have used a periodic 80 × 80 µm 2 simulation domain, i.e., with dimensions similar to a plant cell circumference.…”

Patterning of plant cell wall deposition by cortical microtubules

“…This putative reinforcement mechanism could be tested experimentally by studying nucleation dynamics during protoxylem formation. An experimental approach to assess nucleation is to use fluorescently tagged end binding proteins such as EB1 126,127 and nucleation complexes 128 . When applied during xylem transdifferentiation, these probes would allow for quantification of the location and angles of newly formed microtubules in microtubule gaps and bands.…”

“…Some molecular components involved in metaxylem patterning have been identified 46,49,53-55, , but in depth microtubule dynamics have not been assessed. Studying microtubule dynamics improved understanding how a cortical microtubule array assembles in plant cells 34,128 . These works shows that insight in microtubule dynamics is key to understand the behaviour of a microtubule array.…”

Fluorescent protein marker lines in maize: generation and applications

“…Such studies trace back historically to 3D reconstructions of fixed images at sequential time points, which were used to understand basic subcellular architecture in plants (Donohoe et al, 2013, Staehelin, 1997. Live imaging of FP lines now permits experimental studies of whole organ growth, interactions among neighboring cells, behavior of individual cytoskeletal elements and the ability to trace movement of proteins between cells (Grossmann et al, 2012, Gutierrez et al, 2009, Krebs et al, 2012, Lindeboom et al, 2013, Mathur et al, 2012, Sampathkumar et al, 2011, Teh et al, 2013. With the advent of microfluidic devices, FP markers can be used as biosensors for hormone induction studies during whole root or shoot growth.…”