Investigations into posttranslational modifications of α-tubulin and components of MTOCS in plant cells

Abstract

Microtubules are important components of the plant cytoskeleton. They are dynamic polymers of tubulin which play crucial roles in cell division, cell growth and differentiation and ultimately are responsible for the overall morphology of the plant. For each of these roles, specific microtubule arrays must be formed in a precise place and in coordination with other cellular events. In order to form these arrays, microtubules must be assembled in the correct position and then selectively stabilized. In spite of the importance of these microtubule arrays, little is known about the processes that assemble or stabilize microtubules in higher plant cells. Animals and fungi have distinct cellular organelles--centrosomes, or spindle pole bodies--which nucleate microtubules; however, in plant cells this nucleating function seems to be associated with membranes. Animals also have well described posttranslational and post-polymerizational modifications of tubulin incorporated into stabilized microtubules; however, these modifications have been reported only sporadically in plant cells. In this study, antibodies raised against components found in animal centrosomes and antibodies raised against modified á-tubulin were used to probe plant cells in order to identify microtubule nucleating sites and to determine if posttranslationally modified tubulin is present in plant cells. One posttranslational modification, acetylation, was found in abundance in some conifer but not in angiosperm cells. Another modification, detyrosination, was not present in either angiosperm or gymnosperm cells. These are the first reports of studies of posttranslational modifications of tubulin in gymnosperm cells. The results reported in this study on centrosomal components indicated that their distribution in gymnosperm and bryophyte cells is similar to those reported in angiosperm cells; but that this distribution does not unambiguously identify particular plant microtubule organizing centres.