MUMTAZ BEGUM BINTE MOHAMED HUSSAINBIOLOGICAL SCIENCES2011-11-082011-11-082008-01-28MUMTAZ BEGUM BINTE MOHAMED HUSSAIN (2008-01-28). Genetic control of virulence in Erwinia chrysanthemi pv. Zeae. ScholarBank@NUS Repository.https://scholarbank.nus.edu.sg/handle/10635/28148This study focuses on a bacterial isolate EC1 from rice showing foot rot symptoms. Genetic and phenotype analysis show that EC1 is a member of E. chrysanthemi but displays a unique ability to inhibit rice seeds germination, suggesting it belongs to a rarely characterized pathovar E. chrysanthemi pv. zeae. Transposon disruption of the expI gene encoding the biosynthesis of the quorum sensing signal OHHL significantly enhances the bacterial cell motility, decreases its virulence on potato, and marginally affects its inhibitory activity on rice seeds germination. Further study reveals that EC1 produces an antibiotic-like toxin, which inhibits rice seeds germination. Subsequent mutagenesis and DNA sequence analysis has identified several genes encoding toxin production and regulation. The toxin defective mutants lost the inhibitory activity on rice seeds. These data show for the first time that a novel toxin is a key virulence factor of E. chrysanthemi pv. zeae.enErwinia chrysanthemi pv zeae, expI, toxin, rice seeds germination, OHHL, virulenceThesisNOT_IN_WOS