Plant Physiol, May 2001, Vol. 126, pp. 87-96

Differential mRNA Degradation of Two -Tubulin Isoforms Correlates with Cytosolic Ca²⁺ Changes in Glucan-Elicited Soybean Cells¹

Friedrich Miescher-Institut, P.O. Box 2543, CH-4002 Basel, Switzerland (C.E., L.G.G., G.N.-H., T.B.), and Institut de Biologie Moléculaire des Plantes 12, rue du Général Zimmer, 67 084 Strasbourg cedex, France (A.-C.S.)

Transgenic soybean (Glycine max) culture cells expressing apoaequorin, a Ca²⁺ indicator, were exposed to glucan fragments derived from Phytophthora sojae or to chitin oligomers. The effects of these elicitors on cytosolic Ca²⁺ concentrations and on mRNA levels of two -tubulin isoforms, tubB1 and tubB2, were investigated. The glucan elicitors, to which the cells are known to react with a biphasic cytosolic Ca²⁺ increase, induced a down-regulation of the tubB1 mRNA levels while the tubB2 mRNA level remained constant. The decrease of tubB1 mRNA level was observed after 1 hour of glucan treatment. In contrast, chitin oligomers, known to provoke a monophasic Ca²⁺ increase of short duration, did not affect the tubB1 mRNA level. Pre-incubation with 10 mM 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, an extracellular Ca²⁺ chelator, blocked the cytosolic Ca²⁺ increase as well as the decrease of tubB1 mRNA levels induced by glucan elicitors. Likewise, pre-incubation with 1 mM neomycin, which reduced only the second glucan-induced Ca²⁺ peak, blocked the decrease of tubB1 mRNA level. Experiments with cordycepin, a transcription inhibitor, indicated that glucan fragments induced the degradation of tubB1 mRNA. In conclusion, the glucan-induced cytosolic Ca²⁺ changes are correlated with a strong increase in tubB1 mRNA degradation.