Leaf senescence is accompanied by an early disruption of the microtubule network in Arabidopsis
Keech, O and Pesquet, E and Gutierrez, L and Ahad, A and Bellini, C and Smith, SM and Gardestrom, P, Leaf senescence is accompanied by an early disruption of the microtubule network in Arabidopsis, Plant Physiology, 154, (4) pp. 1710-1720. ISSN 0032-0889 (2010) [Refereed Article]
The dynamic assembly and disassembly of microtubules (MTs) is essential for cell function. Although leaf senescence is a well-documented
process, the role of the MT cytoskeleton during senescence in plants remains unknown. Here, we show that both natural leaf
senescence and senescence of individually darkened Arabidopsis (Arabidopsis thaliana) leaves are accompanied by early degradation of the MT network in epidermis and mesophyll cells, whereas guard cells, which
do not senesce, retain their MT network. Similarly, entirely darkened plants, which do not senesce, retain their MT network.
While genes encoding the tubulin subunits and the bundling/stabilizing MT-associated proteins (MAPs) MAP65 and MAP70-1 were
repressed in both natural senescence and dark-induced senescence, we found strong induction of the gene encoding the MT-destabilizing
protein MAP18. However, induction of MAP18 gene expression was also observed in leaves from entirely darkened plants, showing
that its expression is not sufficient to induce MT disassembly and is more likely to be part of a Ca2+-dependent signaling mechanism. Similarly, genes encoding the MT-severing protein katanin p60 and two of the four putative
regulatory katanin p80s were repressed in the dark, but their expression did not correlate with degradation of the MT network
during leaf senescence. Taken together, these results highlight the earliness of the degradation of the cortical MT array
during leaf senescence and lead us to propose a model in which suppression of tubulin and MAP genes together with induction
of MAP18 play key roles in MT disassembly during senescence.