Cellulose Synthase-Like D (CSLD) proteins, important for tip growth and cell division, are known to generate β-1,4-glucan. However, whether they are propelled in the membrane as the glucan chains they produce assemble into microfibrils is unknown. To address this, we endogenously tagged all eight CSLDs in Physcomitrium patens and discovered that they all localize to the apex of tip-growing cells and to the cell plate during cytokinesis. Actin is required to target CSLD to cell tips concomitant with cell expansion, but not to cell plates, which depend on actin and CSLD for structural support. Like Cellulose Synthase (CESA), CSLD requires catalytic activity to move in the plasma membrane. We discovered that CSLD moves significantly faster, with shorter duration and less linear trajectories than CESA. In contrast to CESA, CSLD movement was insensitive to the cellulose synthesis inhibitor isoxaben, suggesting that CSLD and CESA function within different complexes possibly producing structurally distinct cellulose microfibrils.
- Award ID(s):
- 1817697
- NSF-PAR ID:
- 10175836
- Date Published:
- Journal Name:
- The plant cell
- Volume:
- 32
- Issue:
- 5
- ISSN:
- 1040-4651
- Page Range / eLocation ID:
- 1749-1776
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract The common ancestor of seed plants and mosses contained homo-oligomeric cellulose synthesis complexes (CSCs) composed of identical subunits encoded by a single CELLULOSE SYNTHASE (CESA) gene. Seed plants use different CESA isoforms for primary and secondary cell wall deposition. Both primary and secondary CESAs form hetero-oligomeric CSCs that assemble and function in planta only when all the required isoforms are present. The moss Physcomitrium (Physcomitrella) patens has seven CESA genes that can be grouped into two functionally and phylogenetically distinct classes. Previously, we showed that PpCESA3 and/or PpCESA8 (class A) together with PpCESA6 and/or PpCESA7 (class B) form obligate hetero-oligomeric complexes required for normal secondary cell wall deposition. Here, we show that gametophore morphogenesis requires a member of class A, PpCESA5, and is sustained in the absence of other PpCESA isoforms. PpCESA5 also differs from the other class A PpCESAs as it is able to self-interact and does not co-immunoprecipitate with other PpCESA isoforms. These results are consistent with the hypothesis that homo-oligomeric CSCs containing only PpCESA5 subunits synthesize cellulose required for gametophore morphogenesis. Analysis of mutant phenotypes also revealed that, like secondary cell wall deposition, normal protonemal tip growth requires class B isoforms (PpCESA4 or PpCESA10), along with a class A partner (PpCESA3, PpCESA5, or PpCESA8). Thus, P. patens contains both homo-oligomeric and hetero-oligomeric CSCs.more » « less
-
Summary In seed plants, cellulose is synthesized by rosette‐shaped cellulose synthesis complexes (
CSC s) that are obligate hetero‐oligomeric, comprising three non‐interchangeable cellulose synthase (CESA ) isoforms. The mossPhyscomitrella patens has rosetteCSC s and sevenCESA s, but its common ancestor with seed plants had rosetteCSC s and a singleCESA gene. Therefore, ifP. patens CSC s are hetero‐oligomeric, thenCSC s of this type evolved convergently in mosses and seed plants. Previous gene knockout and promoter swap experiments showed that PpCESA s from class A (PpCESA 3 and PpCESA 8) and class B (PpCESA 6 and PpCESA 7) have non‐redundant functions in secondary cell wall cellulose deposition in leaf midribs, whereas the two members of each class are redundant. Based on these observations, we proposed the hypothesis that the secondary class A and class B PpCESA s associate to form hetero‐oligomericCSC s. Here we show that transcription of secondary class APp s is reduced when secondary class BCESA Pp s are knocked out and vice versa, as expected for genes encoding isoforms that occupy distinct positions within the sameCESA CSC . The class A and class B isoforms co‐accumulate in developing gametophores and co‐immunoprecipitate, suggesting that they interact to form a complexin planta . Finally, secondary PpCESA s interact with each other, whereas three of four fail to self‐interact when expressed in two different heterologous systems. These results are consistent with the hypothesis that obligate hetero‐oligomericCSC s evolved independently in mosses and seed plants and we propose the constructive neutral evolution hypothesis as a plausible explanation for convergent evolution of hetero‐oligomericCSC s. -
Abstract Cellulose, the main component of the plant cell wall, is synthesized by the multimeric cellulose synthase (CESA) complex (CSC). In plant cells, CSCs are assembled in the endoplasmic reticulum or Golgi and transported through the endomembrane system to the plasma membrane (PM). However, how CESA catalytic activity or conserved motifs around the catalytic core influence vesicle trafficking or protein dynamics is not well understood. Here, we used yellow fluorescent protein (YFP)-tagged AtCESA6 and created 18 mutants in key motifs of the catalytic domain to analyze how they affected seedling growth, cellulose biosynthesis, complex formation, and CSC dynamics and trafficking in Arabidopsis thaliana. Seedling growth and cellulose content were reduced by nearly all mutations. Moreover, mutations in most conserved motifs slowed CSC movement in the PM as well as delivery of CSCs to the PM. Interestingly, mutations in the DDG and QXXRW motifs affected YFP-CESA6 abundance in the Golgi. These mutations also perturbed post-Golgi trafficking of CSCs. The 18 mutations were divided into 2 groups based on their phenotypes; we propose that Group I mutations cause CSC trafficking defects, whereas Group II mutations, especially in the QXXRW motif, affect protein folding and/or CSC rosette formation. Collectively, our results demonstrate that the CESA6 catalytic domain is essential for cellulose biosynthesis as well as CSC formation, protein folding and dynamics, and vesicle trafficking.
-
SUMMARY Plant cells and organs grow into a remarkable diversity of shapes, as directed by cell walls composed primarily of polysaccharides such as cellulose and multiple structurally distinct pectins. The properties of the cell wall that allow for precise control of morphogenesis are distinct from those of the individual polysaccharide components. For example, cellulose, the primary determinant of cell morphology, is a chiral macromolecule that can self‐assemble
in vitro into larger‐scale structures of consistent chirality, and yet most plant cells do not display consistent chirality in their growth. One interesting exception is theArabidopsis thaliana rhm1 mutant, which has decreased levels of the pectin rhamnogalacturonan‐I and causes conical petal epidermal cells to grow with a left‐handed helical twist. Here, we show that inrhm1 the cellulose is bundled into large macrofibrils, unlike the evenly distributed microfibrils of the wild type. This cellulose bundling becomes increasingly severe over time, consistent with cellulose being synthesized normally and then self‐associating into macrofibrils. We also show that in the wild type, cellulose is oriented transversely, whereas inrhm1 mutants, the cellulose forms right‐handed helices that can account for the helical morphology of the petal cells. Our results indicate that when the composition of pectin is altered, cellulose can form cellular‐scale chiral structuresin vivo , analogous to the helicoids formedin vitro by cellulose nano‐crystals. We propose that an important emergent property of the interplay between rhamnogalacturonan‐I and cellulose is to permit the assembly of nonbundled cellulose structures, providing plants flexibility to orient cellulose and direct morphogenesis.