CSI1, PATROL1, and exocyst complex cooperate in delivery of cellulose synthase complexes to the plasma membrane

Abstract

SignificanceCellulose is synthesized at the plasma membrane by cellulose synthase complexes (CSCs). The ability to deliver CSCs to discrete sites at the cell surface is critical for cellulose synthesis. We discovered that the de novo secretion of CSCs is mediated by cooperation among a recently identified cellulose synthase interacting protein, exocyst complex, and a plant-specific protein PATROL1 in Arabidopsis thaliana. We present a timeline of events for exocytosis of CSCs. CSCs represent unique cargo proteins that are not conserved in the mammalian or yeast system. Plants offer unique opportunities to characterize the function and regulation of exocytosis that may provide insight into the evolution of exocytosis in eukaryotes.

Secondary cell wall biosynthesis

“…Mutations of two exocyst complex subunits, EXO70A1 and EXO84b, have been shown to cause mislocalization of CESAs and an altered secondary wall deposition Vuka sinovi c et al, 2017), indicating that exocyst complexes are important in the trafficking of CESA complexes and cellulose synthesis. The trafficking of vesicles containing CESA complexes has recently been demonstrated to involve the cooperative actions of CSI1, PATROL1 and the exocyst complexes (Zhu et al, 2018). Two Arabidopsis Golgi-localized STELLO proteins, which are putative glycosyltransferases, are also implicated in the assembly and trafficking of CESA complexes , but the underlying biochemical mechanism is unknown.…”

“…The alignment of CESAs with the underlying cortical microtubules is mediated by CSI1, a cellulose synthase-interactive protein, which was first discovered as a link between primary wall CESAs and cortical microtubules and subsequently shown to be required for the alignment of secondary wall CESAs with cortical microtubules during the early phase of xylem secondary wall thickening (Li et al, 2015;Schneider et al, 2017). CSI1 was recently found to guide the docking of the CESA complex-containing vesicles to specific plasma membrane domains through its interaction with microtubules (Zhu et al, 2018). Additional proteins, such as the KORRIGAN-like glucanases, the COBRA-like glycosylphosphatidylinositol-anchored protein and the chitinase-like proteins (CTLs), are proposed to be involved in modulating cellulose microfibril assembly and crystallinity (Takahashi et al, 2009;Sanchez-Rodriguez et al, 2012;Liu et al, 2013).…”

Association Mapping Considering Allele Dosage: An Example of Forage Traits in an Interspecific Segmental Allotetraploid Urochloa spp. Panel

“…Also, it is involved in the docking of exocytic vesicles with fusion sites on the plasma membrane during secretion (Fendrych et al, 2010). Furthermore, previous findings indicate the role of this macromolecule in cooperation with other proteins for the secretion of cellulose synthase complexes (Zhu et al, 2018), as the cellulose directly related to the fiber content in the plant.…”

Arabidopsis Myosins XI Are Involved in Exocytosis of Cellulose Synthase Complexes

“…An Arabidopsis myosin xi1 xi2 xik triple knockout mutant exhibits an overall dwarf plant phenotype with shorter cell lengths in both dark-grown hypocotyls and light-grown roots, resembling features that are typical of cellulose-deficient mutants and mimicking chemical inhibition of cellulose synthesis (Fagard et al, 2000;Peremyslov et al, 2010;Cai et al, 2014;Bashline et al, 2015). Although cellulose production involves intracellular trafficking and exocytosis of CSCs (Zhu et al, 2018), indications that myosins XI could be responsible are limited. To test whether myosin participates in cellulose production, we measured cellulose content in the previously characterized triple knockout mutant, hereafter referred to as xi3KO (Peremyslov et al, 2010).…”

“…The cytoskeleton is implicated as a central player that coordinates trafficking of CSCs. In addition to choreographing the trajectory of CSCs in the PM, cortical microtubules interact with MASCs through the linker protein CELLULOSE SYNTHASE INTERACTIVE 1 (CSI1) and mark the sites for insertion of newly delivered CSCs (Paredez et al, 2006;Gutierrez et al, 2009;Bringmann et al, 2012;Zhu et al, 2018). However, they do not influence the rate of CSC delivery or abundance of CSCs at the PM, and cellulose content is not altered after treatment with the microtubule-disrupting drug oryzalin (Paredez et al, 2006;Gutierrez et al, 2009;Sampathkumar et al, 2013).…”