Physiological and Molecular Studies of Ethylene Effects on Soybean Root Infection by Soybean Cyst Nematodes

Title of thesis: PHYSIOLOGICAL AND MOLECULAR STUDIES OF ETHYLENE EFFECTS ON SOYBEAN ROOT INFECTION BY SOYBEAN CYST NEMATODES Ping Xue, Master of Science, 2007 Directed By: Dr. Theophanes Solomos, Department of Plant Science and Landscape Architecture Soybean cyst nematode (SCN), Heterodera glycines, is one of the most devastating pests of soybean in the world. Several earlier reports demonstrated that ethylene is involved in nematode feeding cell formation in Arabidopsis and tomato. I investigated whether or not ethylene is involved in SCN feeding cell formation in soybean. My results show that SCN parasitism was increased by treatment of roots with ethylene and inhibited by suppressors of ethylene action or in an ethylene resistant soybean mutant. My results also indicate that excised soybean roots colonized by SCN produced ethylene at 1.5-3 times the rate of non-infected roots between 14 and 22 days post inoculation. To determine if ethylene was being synthesized in feeding cells, an ethylene-responsive promoter fused to a GUS reporter gene was constructed and transformed into soybean roots with Agrobacterium rhizogenes. Overall, the results suggest that ethylene plays an important role in SCN infection in soybean. PHYSIOLOGICAL AND MOLECULAR STUDIES OF ETHYLENE EFFECTS ON SOYBEAN ROOT INFECTION BY SOYBEAN CYST NEMATODES