Keech O, Pesquet E, Gutierrez L, Ahad A, Bellini C, Smith SM, Gardeström P
Leaf senescence Is accompanied by an early disruption of the microtubule network in Arabidopsis
Plant Physiology: 2010 154:1710-1720

Abstract
The dynamic assembly and disassembly of microtubules (MTs) isessential for cell function. Although leaf senescence is a well-documentedprocess, the role of the MT cytoskeleton during senescence inplants remains unknown. Here, we show that both natural leafsenescence and senescence of individually darkened Arabidopsis(Arabidopsis thaliana) leaves are accompanied by early degradationof the MT network in epidermis and mesophyll cells, whereasguard cells, which do not senesce, retain their MT network.Similarly, entirely darkened plants, which do not senesce, retaintheir MT network. While genes encoding the tubulin subunitsand the bundling/stabilizing MT-associated proteins (MAPs) MAP65and MAP70-1 were repressed in both natural senescence and dark-inducedsenescence, we found strong induction of the gene encoding theMT-destabilizing protein MAP18. However, induction of MAP18gene expression was also observed in leaves from entirely darkenedplants, showing that its expression is not sufficient to induceMT disassembly and is more likely to be part of a Ca2+-dependentsignaling mechanism. Similarly, genes encoding the MT-severingprotein katanin p60 and two of the four putative regulatorykatanin p80s were repressed in the dark, but their expressiondid not correlate with degradation of the MT network duringleaf senescence. Taken together, these results highlight theearliness of the degradation of the cortical MT array duringleaf senescence and lead us to propose a model in which suppressionof tubulin and MAP genes together with induction of MAP18 playkey roles in MT disassembly during senescence.

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