Abstract
Cellulose, the most abundant biopolymer on the planet, is synthesized at the plasma membrane of plant cells by the cellulose synthase complex (CSC). Cellulose is the primary load-bearing polysaccharide of plant cell walls and enables cell walls to maintain cellular shape and rigidity. The CSC is comprised of functionally distinct cellulose synthase A (CESA) proteins, which are responsible for synthesizing cellulose, and additional accessory proteins. Moreover, CESA-like (CSL) proteins are proposed to synthesize other essential non-cellulosic polysaccharides that comprise plant cell walls. The deposition of cell-wall polysaccharides is dynamically regulated in response to a variety of developmental and environmental stimuli, and post-translational phosphorylation has been proposed as one mechanism to mediate this dynamic regulation. In this review, we discuss CSC composition, the dynamics of CSCs in vivo, critical studies that highlight the post-translational control of CESAs and CSLs, and the receptor kinases implicated in plant cell-wall biosynthesis. Furthermore, we highlight the emerging importance of post-translational phosphorylation-based regulation of CSCs on the basis of current knowledge in the field.
Highlights
Plant cell walls are complex polysaccharide-rich extracellular matrices that surround all plant cells and critically influence basic cellular growth processes, such as cell expansion, cell division, and the acquisition of cell shape [1,2,3]
cellulose synthase complex (CSC) subunits are localized to the Golgi apparatus, where complex assembly is assisted by STELLO proteins [64] before CSCs are trafficked to the plasma membrane via post-Golgi compartments called small cellulose synthase A (CESA) compartments (SmaCC) [58] or MT-associated cellulose synthase compartments (MASCs) [43,44]
It is important to note that Cellulose synthase A7 (CESA7)-containing CSCs have been imaged by an inducible expression system in live Arabidopsis seedlings [74], and these experiments revealed that secondary cell walls (SCWs) CSCs exhibit showed increased stability of the phosphorylated CESA7 N-terminus, suggesting that phosphorylation may play a role in destabilizing CESA proteins, resulting in their regulated degradation by the 26S
Summary
Plant cell walls are complex polysaccharide-rich extracellular matrices that surround all plant cells and critically influence basic cellular growth processes, such as cell expansion, cell division, and the acquisition of cell shape [1,2,3]. The precise chemical composition of the cell wall changes during growth and development or in response to environmental stresses [9], but PCWs typically consist of three polysaccharide networks: cellulose, neutral hemicelluloses, and acidic pectins. Plant growth and development is a consecutive process consisting of both cell-division and cell-expansion events, and cellulose deposition plays key roles in these processes [16]. Cellulose biosynthesis plays a key role in cell expansion, whereby cellulose deposition typically occurs perpendicular to the axis of cell growth and elongation [23]. We mainly focus on the post-translational regulation of cellulose biosynthesis and the biosynthetic regulation of other cell-wall polymers
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