INDUCTION OF CDC2A AND CYC1AT EXPRESSION IN ARABIDOPSIS-THALIANA DURING EARLY PHASES OF NEMATODE-INDUCED FEEDING CELL-FORMATION

Root-knot and cyst nematodes are plant parasites that induce large mul tinucleated feeding cells in the roots of their hosts. Cytological obs ervations have shown that root-knot nematodes induce giant cells by cy cles of mitosis without cytokinesis whereas cyst nematodes provoke cel l wall degradation leading to the formation of a large syncytium. This study was intended to characterize and compare the ability of both ty pes of nematodes to induce progression through the cell cycle. For thi s purpose, the expression, upon nematode infection, of two cell cycle markers was followed: a marker for division competence, the cyclin-dep endent kinase cdc2a and a marker for the G2 phase, the mitotic cyclin cyc1At. For both types of nematodes, transcriptional activation of the se markers was correlated with early phases of feeding cell developmen t. Using molecular markers, it was thus possible to confirm and extend the observations of repeated mitosis in root-knot nematode induced gi ant cells. Surprisingly, promoter activation of both cdc2a and cyc1At markers was also found upon cyst nematode infection, in feeding cells in which mitosis has not been clearly reported. Incorporation of triti ated thymidine in these syncytia confirms that they progress through t he S phase of the cell cycle. One possibility is that cyst nematodes i nduce cycles of DNA endoreduplication shunting the M phase. Despite ob vious differences in ontogeny, common Molecular mechanisms, involving cycles of DNA endoreduplication and cdc2a and cyc1At expression, might thus be involved in the formation of a giant cell or a syncytium.