Virtually all eukaryotic α-tubulins harbour a C-terminal tyrosine that can be reversibly removed and religated, catalysed by a specific tubulin–tyrosine carboxypeptidase (TTC) and a specific tubulin–tyrosine ligase (TTL), respectively. The biological function of this post-translational modification has remained enigmatic. 3-nitro-L-tyrosine (nitrotyrosine, NO2Tyr), can be incorporated into detyrosinated α-tubulin instead of tyrosine, producing irreversibly nitrotyrosinated α-tubulin. To gain insight into the possible function of detyrosination, the effect of NO2Tyr has been assessed in two plant model organisms (rice and tobacco). NO2Tyr causes a specific, sensitive, and dose-dependent inhibition of cell division that becomes detectable from 1 h after treatment and which is not observed with non-nitrosylated tyrosine. These effects are most pronounced in cycling tobacco BY-2 cells, where the inhibition of cell division is accompanied by a stimulation of cell length, and a misorientation of cross walls. NO2Tyr reduces the abundance of the detyrosinated form of α-tubulin whereas the tyrosinated α-tubulin is not affected. These findings are discussed with respect to a model where NO2Tyr is accepted as substrate by TTL and subsequently blocks TTC activity. The irreversibly tyrosinated α-tubulin impairs microtubular functions that are relevant to cell division in general, and cell wall deposition in particular.

The biological effects of electric pulses with low rise time, high field strength, and durations in the nanosecond range (nsPEFs) have attracted considerable biotechnological and medical interest. However, the cellular mechanisms causing membrane permeabilization by nanosecond pulsed electric fields are still far from being understood. We investigated the role of actin filaments for membrane permeability in plant cells using cell lines where different degrees of actin bundling had been introduced by genetic engineering. We demonstrate that stabilization of actin increases the stability of the plasma membrane against electric permeabilization recorded by penetration of Trypan Blue into the cytoplasm. By use of a cell line expressing the actin bundling WLIM domain under control of an inducible promotor we can activate membrane stabilization by the glucocorticoid analog dexamethasone. By total internal reflection fluorescence microscopy we can visualize a subset of the cytoskeleton that is directly adjacent to the plasma membrane. We conclude that this submembrane cytoskeleton stabilizes the plasma membrane against permeabilization through electric pulses.

No abstract

No abstract

The detyrosination/retyrosination cycle is the most common post-translational modification of α-tubulin. Removal of the conserved C-terminal tyrosine of αtubulin by a still elusive tubulin tyrosine carboxypeptidase, and religation of this tyrosine by a tubulin tyrosine ligase (TTL), are probably common to all eukaryotes. Interestingly, for plants, the only candidates qualifying as potential TTL homologs are the tubulin tyrosine ligase-like 12 proteins. To get insight into the biological functions of these potential TTL homologs, we cloned the rice TTL-like 12 protein (OsTTLL12) and generated overexpression OsTTLL12-RFP lines in both rice and tobacco BY-2 cells. We found, unexpectedly, that overexpression of this OsTTLL12-RFP increased the relative abundance of detyrosinated α-tubulin in both coleoptile and seminal root, correlated with more stable microtubules. This was independent of the respective orientation of cortical microtubule, and followed by correspondingly changing growth of coleoptiles and seminal roots. A perturbed organization of phragmoplast microtubules and disoriented cell walls were further characteristics of this phenotype. Thus, the elevated tubulin detyrosination in consequence of OsTTLL12 overexpression affects structural and dynamic features of microtubules, followed by changes in the axiality of cell plate deposition and, consequently, plant growth.