Cellulose synthase interactive protein 1 (CSI1) links microtubules and cellulose synthase complexes

Abstract

Cellulose synthase (CESA) complexes can be observed by live-cell imaging to move with trajectories that parallel the underlying cortical microtubules. Here we report that CESA interactive protein 1 (CSI1) is a microtubule-associated protein that bridges CESA complexes and cortical microtubules. Simultaneous in vivo imaging of CSI1, CESA complexes, and microtubules demonstrates that the association of CESA complexes and cortical microtubules is dependent on CSI1. CSI1 directly binds to microtubules as demonstrated by in vitro microtubule-binding assay.cell expansion | cellulose | cell walls T he control of plant cell shape, and ultimately morphology, is achieved mostly by anisotropic expansion that results from the combined effects of uniform outward turgor pressure and nonuniform counteracting resistance exerted by cell walls. Cellulose microfibrils, as the major load-bearing polymers in cell walls, are the predominant component enforcing the asymmetric cell expansion (1). In growing cells, cellulose microfibrils are laid down transversely to the axis of elongation, thus forming a spring-like structure that reinforcing the cell laterally and favoring longitudinal expansion. The predominant theory of how plant cells establish cellulose microfibril orientation has implicated the cortical microtubules (1-7). Cortical microtubules were reported to be oriented in parallel to the cellulose microfibrils during cellulose synthesis in many different cell types and organisms (2, 4), and disruption of cortical microtubules using various microtubule inhibitors disorganizes the pattern of cellulose microfibril deposition (8-11).A recent advance in testing the role of microtubules in cellulose synthesis was made by visualizing cortical microtubule and cellulose synthase (CESA) complexes simultaneously (12). CESA complexes can be directly observed by live-cell imaging moving through the plasma membrane on trajectories that parallel the underlying cortical microtubules. When the microtubule array is disorganized by exposure to oryzalin, a microtubuledisrupting herbicide, the trajectories of the CESA particles change accordingly (12). These experiments provide convincing evidence to support the idea that the orientation of cortical microtubules specifies the spatial orientation in which cellulose microfibrils are deposited. However, this concept is an oversimplification because there are circumstances where the alignment of cellulose microfibrils apparently occurs independently of microtubules and the mechanism of interaction between microtubules and cellulose synthase complexes has not been described (2). Here, we report that the recently identified CESA interactive protein 1 (CSI1) mediates an interaction between microtubules and cellulose synthase. Results CSI1Colocalizes with Cortical Microtubules. CESA complexes move along trajectories that closely parallel microtubules (12-15). We examined whether CSI1 coaligns with microtubules in a transgenic line bearing both YFP-TUA5 (an α-tubulin) and red fluorescent protein (RFP)-CSI...

Indaziflam Herbicidal Action: A Potent Cellulose Biosynthesis Inhibitor

“…Rather, the movement of CESA particles was proposed to be a function of a polymerization force generated by the translocating glucan chain (Diotallevi and Mulder, 2007). The PM movement of CESA particles in untreated cells was bidirectional with an average velocity of 336 6 167 nm min 21 , which is consistent with numerous prior studies (Paredez et al, 2006;Bischoff et al, 2009;Crowell et al, 2009;Gutierrez et al, 2009;Gu et al, 2010;Li et al, 2012). After treatment with indaziflam, YFP:CESA6 velocity was reduced to 119 6 95 nm min 21 (Fig.…”

“…In the molecular rail hypothesis proposed by Giddings and Staehelin (1988), CESA particles are guided by the underlying cortical MTs. The coincidence between PM CESA particles and MTs is normally around 70% to 80% (Paredez et al, 2006;Li et al, 2012). The average colocalization rate over three experimental runs (total n = 544) between YFP:CESA6 particles and RFP:TUA5 after indaziflam treatment was 53% 6 4%.…”

“…In csi1 mutants, CESA particles in the PM were found to display reduced velocity and their association with MTs was completely disrupted (Gu et al, 2010;Li et al, 2012). Because this cellular phenotype is similar to what we observed in wild-type seedlings treated with indaziflam, we explored the effect of indaziflam on the behavior of CESA particles in the csi1-3 mutant background.…”

“…Reduced CESA Velocity after Indaziflam Treatment Is CSI1 Independent CSI1 was identified as a primary linker protein between MTs and CSCs (Gu et al, 2010;Bringmann et al, 2012;Lei et al, 2012;Li et al, 2012). In csi1 mutants, CESA particles in the PM were found to display reduced velocity and their association with MTs was completely disrupted (Gu et al, 2010;Li et al, 2012).…”

Complexes with Mixed Primary and Secondary Cellulose Synthases Are Functional in Arabidopsis Plants

“…Fluorescently labeled CESAs are also seen in Golgi bodies and in small microtubuleassociated compartments (SMaCCs), which are implicated in trafficking CESA from the Golgi to the plasma membrane (Crowell et al, 2009;Gutierrez et al, 2009). Although the association of CESA complexes with microtubules appears to be mediated by the cellulose synthase interactive protein 1 (Li et al, 2012), the timing and mechanism of CESA complex assembly remains an open question.…”