SUBCELLULAR LOCALIZATION OF THE CF-9 RESISTANCE PROTEIN
SUBCELLULAR LOCALISATION OF THE Cf-9 RESISTANCE PROTEIN
M BENGHEZAL and DA JONES
Plant Cell Biology, Research School of Biological Sciences, Australian National University, PO Box 475, Canberra ACT 2601, Australia
Background and objectives
Our objective is to investigate the cellular localization of Cf-9. Assuming that Cf-9 is the receptor for the Avr9 avirulence peptide, which is secreted into the apoplasm of infected tomato leaves, it is reasonable to infer a plasma membrane localization of Cf-9. Surprisingly, the C-terminus of Cf-9 has the mammalian and yeast KKXX motif for the retrieval of membrane-bound proteins from the Golgi apparatus to the endoplasmic reticulum . To test whether Cf-9 is retrieved to the ER and whether the KKXX motif is functional in plants, the green fluorescent protein of jellyfish (GFP) has been fused to Cf-9 and six different constructs, one of which contains a KSXX motif, have been introduced into Arabidopsis and tomato.The subcellular localization of these different fusion proteins will be tested in the transgenic plants by confocal light microscopy. These fusion proteins have also been expressed transiently in tobacco protoplasts and inducibly in yeast.
Results and conclusions
The KKXX motif of Cf-9 is functional in yeast and tobacco cells, which would argue firstly, that Cf-9 behaves as a retrievable protein, and secondly, that plants, like mammals and yeast, use this retrieval motif. Hence, if Cf-9 is also localized in the ER of tomato, it would render the hypothesis of direct interaction of Avr9 peptide with Cf-9 protein on the cell surface more unlikely, and we may have to postulate an interaction elsewhere or even an indirect interaction.