Plant chaperonins: a role in microtubule-dependent wall formation?

The cytosolic chaperonin containing t-complex peptide-1 (CCT) is involved i n the correct folding of newly synthetized actin and tubulin molecules. To get insight into potential additional functions of plant CCT, the localizat ion of the subunit CCT epsilon was Followed throughout cell cycle, cell elo ngation, and cell differentiation in the tobacco cell culture VBI-O with re lation to the microtubular cytoskeleton by double -immunofluorescence and c onfocal microscopy. The CCT epsilon subunit was found to colocalize with si tes of microtubule nucleation such as nuclear envelope and preprophase band . In addition, CCT epsilon was associated with tubulin in sites of elevated wall synthesis such as phragmoplast or along secondary-wall thickenings. C CT epsilon and its substrate tubulin were round to be soluble during period s of cytoskeletal dynamics, whereas sedimentable, vesicle-hound forms of CC T epsilon and tubulin prevailed during cell differentiation. The sedimentab ility of CCT epsilon was increased by calcium, whereas it was detached from microsomes by ATP. CCT epsilon can bind to both polymerized microtubules a nd tubulin dimers. These data suggest an additional function of plant CCT i n microtubule-driven transport of vesicles that contain cell-wall material.