Details

Autor(en) / Beteiligte

• Blatt, M.R
• Grabov, A
• Brearley, J
• Hammond-Kosack, K
• Jones, J.D.G

Titel

K+ channels of Cf-9 transgenic tobacco guard cells as targets for Cladosporium fulvum Avr9 elicitor-dependent signal transduction

Ist Teil von

• The Plant journal : for cell and molecular biology, 1999-08, Vol.19 (4), p.453-462

Ort / Verlag

Oxford, UK: Blackwell Science Ltd

Erscheinungsjahr

1999

Link zum Volltext

Quelle

Wiley Online Library

Beschreibungen/Notizen

• The cf-9 gene encodes an extracytosolic leucine-rich repeat (LRR) protein that is membrane anchored near its C-terminus. The protein confers resistance in tomato to races of the fungus Cladosporium fulvum expressing the corresponding avirulence gene Avr9. In Nicotiana tabacum the Cf-9 transgene confers sensitivity to the Avr9 elicitor, and leads on elicitation to a subset of defence responses qualitatively similar to those normally seen in the tomato host. One of the earliest responses, both in the native and transgenic hosts, results in K(+) salt loss from the infected tissues. However, the mechanism(s) underlying this solute flux and its control is poorly understood. We have explored the actions of Avr9 on Cf-9 transgenic Nicotiana using guard cells as a model. Much detail of guard cell ion channels and their regulation is already known. Measurements were carried out on intact guard cells in epidermal peels, and the currents carried by inward- (l(k,in)) and outward-rectifying (I(k,out)) K(+) channels were characterized under voltage clamp. Exposures to Avr9-containing extracts resulted in a 2.5- to 3-fold stimulation of l(k,out) and almost complete suppression of l(k,in) within 3-5 min. The K(+) channel responses were irreversible. They were specific for the Avr9 elicitor, were not observed in guard cells of Nicotiana lacking the Cf-9 transgene and, from kinetic analyses, could be ascribed to changes in channel gating. Both K(+) channel responses were found to be saturable functions of Avr9 concentration and were completely blocked in the presence of 0.5 micromolar staurosporine and 100 micromolar H7, both broad-range protein kinase antagonists. These results demonstrate the ability of the Cf-9 transgene to couple Avr9 elicitation specifically to a concerted action on two discrete K(+) channels and they indicate a role for protein phosphorylation in Avr9/Cf-9 signal transduction leading to transport control.