|Ibekwe, Abasiofiok - Mark|
Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/11/2006
Publication Date: 2/15/2007
Citation: Yang, S., Zhang, Q., Chorkowski, A.O., Glick, B.R., Ibekwe, A.M., Cooksey, D.A., Yang, C.H. 2007. Global effect of indole-3-acetic acid biosynthesis on multiple virulence factors of erwinia chrysanthemi 3937. Applied and Environmental Microbiology. Feb 2007: 1079-1088 Interpretive Summary: Erwinia chrysanthemi is an opportunistic pathogen that causes soft-rot, wilts and blight diseases on a wide range of plant species. Several factors that cause these diseases have been discovered in E. chrysanthemi including extracellular enzymes and siderophore-dependent iron uptake systems. We demonstrated that E. chrysanthemi 3937 has the capacity to produce plant hormones that may enhance bacterial fitness in planta, stimulate plant growth, and increased the release of plant metabolites that the bacteria can utilize. Understanding of the genetic factors of E. chrysanthemi that enable it to colonize plants and cause disease will facilitate the development of intervention strategies to reduce E. chrysanthemi spread on plants. The mechanisms for the inhibition of local tissue in IAA over-producer E. chrysanthemi_ iaaM strain and enhanced local maceration ability of iaaM::KAN mutant showed that the mutant reduced IAA production and the reintroduction of the two homologous genes will revert to more production of IAA. This information will be useful to scientists, plant pathologist, and extension agents in developing and education farmers on control strategies for soft-rot, wilts and blight diseases.
Technical Abstract: Production of the plant hormone indoleacetic-3-acid (IAA) is widespread among plant-associated microorganisms and it is important for pathogenesis in hyperplasia-inducing bacteria. It may also benefit bacteria by enhancing bacteria fitness in planta, stimulating plant growth and increasing the release of plant metabolites that the bacteria can utilize. Microorganisms possess several different IAA biosynthetic pathways. The indole-3-acetamide (IAM) pathway is employed mostly by pathogenic bacteria, and the indole-3-pyruvatic acid (IPyA) pathway is the major IAA biosynthesis pathway by plant growth-promoting bacteria. The non-gall-forming phytopathogen E. chrysanthemi 3937 possesses iaaM and iaaH gene homologues and has the capacity to produce IAA through the IAM pathway. In this work, the iaaM insertional mutant (iaaM::KAN) was constructed and further characterized. Analysis of IAA deficient mutant iaaM::KAN indicated that the iaaM operon played multiple roles on IAA production and other phenotypes. iaaM::KAN mutants reduced IAA production in minimal medium supplemented with L-tryptophan and lost the capability to form a pellicle, which can be restored by putting the iaaM and iaaH expressing plasmid into the iaaM::KAN mutant. The spreading motility and pectate lyase production in vitro and in host plant African violet cv. Gaugil were enhanced in both the iaaM::KAN mutant and IAA over-producer Ech_iaaM strains. In addition, the in planta multiplication ability of the iaaM::KAN mutant and Ech_iaaM were diminished. Although the local maceration symptoms of the iaaM::KAN mutant were enhanced in the host plant African violet cv. Gaugil, the IAA over-producer strain Ech_iaaM had reduced local maceration ability.