Phytochrome Regulation of Cellulose Synthesis in Arabidopsis

Abstract

Plant development is highly plastic and dependent on light quantity and quality monitored by specific photoreceptors. Although we have a detailed knowledge of light signaling pathways, little is known about downstream targets involved in growth control. Cell size and shape are in part controlled by cellulose microfibrils extruded from large cellulose synthase complexes (CSCs) that migrate in the plasma membrane along cortical microtubules. Here we show a role for the red/far-red light photoreceptor PHYTOCHROME B (PHYB) in the regulation of cellulose synthesis in the growing Arabidopsis hypocotyl. In this organ, CSCs contains three distinct cellulose synthase (CESA) isoform classes: nonredundant CESA1 and CESA3 and a third class represented by partially redundant CESA2, CESA5, and CESA6. Interestingly, in the dark, depending on which CESA subunits occupy the third position, CSC velocity is more or less inhibited through an interaction with microtubules. Activation of PHYB overrules this inhibition. The analysis of cesa5 mutants shows a role for phosphorylation in the control of CSC velocity. These results, combined with the cesa5 mutant phenotype, suggest that cellulose synthesis is fine tuned through the regulated interaction of CSCs with microtubules and that PHYB signaling impinges on this process to maintain cell wall strength and growth in changing environments.

Functional Analysis of Cellulose and Xyloglucan in the Walls of Stomatal Guard Cells of Arabidopsis

“…Stomatal pore dimensions, guard cell pair dimensions, and guard cell dimensions in wild-type and xxt1 xxt2 plants during FC or ABA treatment Stomatal aperture, stomatal pore length, ratio of aperture to pore length, guard cell pair height, guard cell pair width, aspect ratio of guard cell pairs (height to width), ratio of aperture to guard cell pair width, guard cell diameter, and guard cell length were measured on a single stomate basis using epidermal peels from 3-to 4-week-old plants. suggesting that cellulose biosynthesis might be a downstream target of phytochrome B-involved light signaling pathways in cesa6 prc1-1 hypocotyls (Bischoff et al, 2011). The discrepancy in the effect of darkness on CSC motility between our results in guard cells and the previous results in cesa6 prc1-1 hypocotyls (Bischoff et al, 2011) could be attributed to the tissue specificity of dark-responsive signaling or different durations of dark treatment.…”

“…suggesting that cellulose biosynthesis might be a downstream target of phytochrome B-involved light signaling pathways in cesa6 prc1-1 hypocotyls (Bischoff et al, 2011). The discrepancy in the effect of darkness on CSC motility between our results in guard cells and the previous results in cesa6 prc1-1 hypocotyls (Bischoff et al, 2011) could be attributed to the tissue specificity of dark-responsive signaling or different durations of dark treatment. We speculate that the increase in GFP-CESA3 speed in guard cells bordering closed stomata and in neighboring pavement cells, in light of the findings from previous studies (Bischoff et al, 2011;Boex-Fontvieille et al, 2014), might be attributed, at least in part, to posttranslational modulation of CESA3 CSCs migrate at the plasma membrane in linear trajectories coaligned with underlying cortical MTs, the presence of which is not a strict requirement for CSC motility (Paredez et al, 2006;Chen et al, 2010).…”

“…Live-cell imaging of fluorescent protein-tagged CESAs has demonstrated that cortical microtubules (MTs) dictate the trajectories of CSCs, which move bidirectionally with an average speed of approximately 330 nm min 21 along linear tracks that are aligned with MTs (Paredez et al, 2006). However, the motility of CSCs is not strictly dependent on the presence of MTs (Paredez et al, 2006): lower MT abundance in Arabidopsis etiolated hypocotyl epidermal cells can result in a higher proportion of CSCs that track independently of MTs and an increase in CSC speed (Chen et al, 2010;Bischoff et al, 2011;Fujita et al, 2011), suggesting that CSCs might move faster in the absence of MT guidance. Despite these advances in our understanding of CSC behavior, CSC dynamics have not been reported in guard cells, and it also remains unknown whether CSC distribution, motility, and/or association with MTs are altered as stomata open or close, during which MTs in guard cell have been reported to undergo dynamic rearrangements and changes in abundance (Eisinger et al, 2012a(Eisinger et al, , 2012b.…”

Cellulose microfibril crystallinity is reduced by mutating C-terminal transmembrane region residues CESA1 A903V and CESA3 T942I of cellulose synthase

“…The effect that genetic mutations have on cellulose polymerization rates can therefore be explored by examining the displacement velocity of fluorescently labeled CESA at the PM. Although previous analyses of the CESA velocity in cellulose deficient or MT mutants have suggested that polymerization rate can be altered, these studies have not addressed the influence that microfibril structure could impart on CESA velocity (21)(22)(23)(24).…”

Anisotropic Cell Expansion Is Affected through the Bidirectional Mobility of Cellulose Synthase Complexes and Phosphorylation at Two Critical Residues on CESA3

“…Phosphorylation of CESA5 modulates migration of CESA complexes containing the CESA6-related isoform, CESA5, which is coordinated by phytochrome activation (Bischoff et al, 2011). Therefore, it was of interest to examine if and how phosphorylation of CESA3 regulates interactions of CESA particles with cortical microtubules, particularly microtubule-guided bidirectional synthesis and deposition of cellulose microfibrils.…”