Zhong, G.Y., Kenedy-Leigh Centre for Horticultural Research, Faculty of Agriculture, Hebrew University of Jerusalem, Rehovot, 76100, Israel
Riov, J., Kenedy-Leigh Centre for Horticultural Research, Faculty of Agriculture, Hebrew University of Jerusalem, Rehovot, 76100, Israel
Goren, R., Kenedy-Leigh Centre for Horticultural Research, Faculty of Agriculture, Hebrew University of Jerusalem, Rehovot, 76100, Israel
Holland, D., Fruit Tree Breeding Department, Institute of Horticulture, Agricultural Research Organization, Volcani Center, Bet-Dagan 50250, Israel

Ethylene plays a key role in the control of fruit abscission. Treatment of citrus fruit abscission zone with exogenous ethylene induces cell proliferation and the production of cellulases and polygalacturonases. Our aim is to identify genes that function in early steps of ethylene induced abscission. Our working hypothesis is that protein kinases (specifically serine/threonine kinases) might be involved in early stages of ethylene perception by cells within the abscission zone. By utilizing RT-PCR technology with degenerate primers corresponding to conserved regions of serine/threonine protein kinase genes and mRNA from ethylene treated citrus fruit abscission zone, we isolated truncated genes that are homologous to plant and mammalian serine/threonine protein kinase genes. The full length of the coding sequences of the genes CMAPK1 and CMAPK2 was obtained and analyzed. CMAPK1 and CMAPK2 are highly homologous to mammalian and plant MAP kinases that are specifically involved in response to environmental stresses. Northern blot analysis indicates that CMAPK1 and CMAPK2 genes respond differentially to treatment with ethylene. While mRNA corresponding to CMAPK2 increased already after 1 hour ethylene treatment, mRNA corresponding to CMAP1 increased only after 8 hours. Both genes reached their peak 8 hours after ethylene treatment. The results obtained suggest that the genes identified are involved in response to ethylene in citrus fruit abscission zone and that MAP kinase genes might play, among other functions, a role in the abscission process.