Phosducin-Like Protein 3 is required for microtubule-dependent steps of cell division but not for meristem growth in Arabidopsis

Given the central role of cell division in meristems, one might expect meristem growth to be regulated by mitotic checkpoints, including checkpoints for correct microtubule function. Here, we studied the role of two close Phosducin-Like Protein 3 homologs from Arabidopsis thaliana (PLP3a and PLP3b) in the microtubule assembly pathway and determined the consequences of inhibiting PLP3a and PLP3b expression in the meristem. PLP3 function is essential in Arabidopsis: impairing PLP3a and PLP3b expression disrupted microtubule arrays and caused polyploidy, aneuploidy, defective cytokinesis, and disoriented cell growth. Consistent with a role in microtubule formation, PLP3a interacted with beta-tubulin in the yeast two-hybrid assay and, when overexpressed, increased resistance to drugs that inhibit tubulin polymerization. Inhibition of PLP3 function targeted to the meristem caused severe mitotic defects, but the cells carried on cycling through DNA replication and abortive cytokinesis. Thus, we showed that PLP3 is involved in microtubule formation in Arabidopsis and provided genetic evidence that cell viability and growth in the meristem are not subordinate to successful completion of microtubule-dependent steps of cell division.