The Regulation of Cellulose Biosynthesis in Plants

Joanna K. Polko; Joseph J. Kieber

doi:10.1105/tpc.18.00760

Published February 2019. DOI: https://doi.org/10.1105/tpc.18.00760

Article Figures & Data

Figures

Tables
Additional Files

Download figure
Open in new tab
Download powerpoint
Figure 1.
Schematic Representations of the Structure of a CESA Protein and a CSC.
(A) Domain structure of a CESA. The intracellular N-terminal domain contains a Zn binding domain and a variable region and is followed by two transmembrane domains. The large cytoplasmic central catalytic domain is divided into the conserved region, which flanks the plant-specific region on both sides, the variable region(s), which includes the class-specific region, and the conserved region(s). The six subsequent transmembrane domains are followed by the cytoplasmic C-terminal domain. CESA1 phosphorylations on various Ser and Thr residues are indicated (source: PhosPhAt 4.0, Zulawski et al., 2013; and references in the text). Several cysteines in the cytoplasmic loop and within the C-terminal domain that are s-acylated in CESA7 (Kumar 2016b) are depicted in pink. C, cellulose chain; CR1, conserved region 1; CR2, conserved region 2; P-CR, plant-specifc region; S, Ser; T, Thr.
(B) A schematic representation of a CSC consisting of 18 individual CESA proteins. The model is consistent with the rules outlined by Hill et al. (2014) and assumes that: a CSC is composed of six lobes that contain three CESA isoforms; the contacts between different isoforms is conserved; and the number of CESAs in each lobe is divisible by three.
(C) A model of a cellulose microfibril consisting of five layers of cellulose chains in a “34443” arrangement (C = cellulose chain).
Download figure
Open in new tab
Download powerpoint
Figure 2.
A Cartoon of CSC Trafficking and the Other Components of the CSC Machinery.
CSCs are assembled in the Golgi apparatus where they physically interact with STL proteins that assist their assembly and distribution in the Golgi. CSCs move through the TGN and follow the exocytosis route to the PM, where their insertion sites coincide with the pausing of the Golgi along the CMTs. The insertion of CSCs in the PM is preceded by POM2/CSI1, the exocyst complex, and PTL, which are required for CSC delivery. The CESA-interacting proteins SHOU4/4L negatively affect CSC exocytosis. POM2/CSI1 proteins also act as linkers between CSCs and CMTs and are necessary for the formation of SmaCCs/MASCs. The CC1 and CC2 belong to the CSCs, associate with SmaCCs/MASCs under salt stress and mediate the CMT and CSC dynamics, allowing for their recovery. CMU proteins regulate proper CMT spacing during cellulose biosynthesis. KOR is a component of CSCs required for optimal cellulose biosynthesis and COB is necessary for proper microfibril orientation. The SOS5 and FEI1/2 leucine-rich repeat-RLKs mediate cellulose biosynthesis and CrRLK1L THE1 inhibits cell expansion upon perturbation of cellulose biosynthesis. CSCs undergo CME that requires the AP2 complex and TPLATE complex members such as TWD40-1, TPLATE, and TML. The endocytosed CSCs may undergo recycling back to the PM or might be targeted for degradation.

View popup

Table 1. CESA Interacting Proteins

Protein	Putative role	Partner CESA	Method^a	Reference
KORRIGAN	Cellulose synthesis and CSC trafficking	CESA1	Gel filtration,	(Vain et al., 2014)
		CESA3	Split-ubiquitin for membrane proteins,	(Zhu et al., 2018)
		CESA6	BiFC,	(Mansoori et al., 2014)
		CESA4	GFP-TRAP/MS,
		CESA8	Y2H
CC1/2	Cellulose synthesis during salt stress	CESA1	Split-ubiquitin assay in yeast	(Endler et al., 2015)
		CESA3
		CESA6
POM2/CSI1	CSC-CMT interaction; formation of SmaCCs/MASCs; CSC trafficking	CESA1CESA3	Y2H, GST pull-down	(Gu et al., 2010)(Lei et al., 2015)
POM2/CSI1		CESA6	Y2H, GST pull-down
AP2M/µ2	CSC endocytosis	CESA1	Split-ubiquitin Y2H,	(Bashline et al., 2013)
		CESA3	GST pull-down
		CESA6
Sec5B	CSC exocytosis	CESA6	Y2H,	(Zhu et al., 2018)
Sec10			GFP-TRAP/MS
Sec6
Sec15B
Sec8
Sec3A
Exo84B
Exo70B1
Exo70A1
PTL1
TML	CSC endocytosis	CESA6	Co-IP, BiFC	(Sanchez-Rodriguez et al., 2018)
TPLATE	CSC endocytosis	CESA6	Co-IP, BiFC	(Sanchez-Rodriguez et al., 2018)
BIN2	CESA phosphorylation; regulation of CESA activity	CESA1	in vitro protein kinase assay	(Sanchez-Rodriguez et al., 2017)
SHOU4	CSC exocytosis	CESA1	Y2H, Co-IP	(Polko et al., 2018)
		CESA3
		CESA6

↵a The methods shown are not necessarily for all the partner CESAs indicated. BIFC, bimolecular fluorescence complementation; Co-IP, co-immunoprecipitation; GST, glutathione S-transferase; Y2H, yeast two-hybrid.