Abstract
Isoflavonoids and steady-state mRNA levels of phenylalanine ammonia-lyase, chalcone isomerase, and isoflavone reductase were followed during a rapid, nearly synchronous infection of alfalfa (Medicago sativa L.) roots by the vesicular arbuscular fungus Glomus intraradices (Schenck & Smith) to test whether previously indicated suppression of the host defense response is regulated by changes in the steady-state mRNA level. Relative amounts of steady-state phenylalanine ammonia-lyase mRNA in the mycorrhizal roots doubled between d 14 and 18 and then immediately declined by 75% to reach and maintain a value lower than the control roots through d 21. Relative levels of chalcone isomerase mRNA in the inoculated roots increased 6-fold between d 14 and 17 and then decreased rapidly to the control level. Isoflavone reductase mRNA was not induced by mycorrhizal colonization. High-performance liquid chromatography, proton-nuclear magnetic resonance, and fast atom bombardment-mass spectrometry analyses showed consistent increases in formononetin levels and transient increases in medicarpin-3-O-glycoside and formononetin conjugates in the inoculated roots when colonization began. As colonization increased, levels of formononetin conjugates declined in mycorrhizal roots below those in uncolonized controls. Medicarpin aglycone, an alfalfa phytoalexin normally associated with pathogenic infections, was not detected at any stage. These findings supply detailed evidence that, during early colonization of plant roots by symbiotic Glomus, defense transcripts are induced and then subsequently suppressed.
Full Text
The Full Text of this article is available as a PDF (1.0 MB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Dakora F. D., Joseph C. M., Phillips D. A. Alfalfa (Medicago sativa L.) Root Exudates Contain Isoflavonoids in the Presence of Rhizobium meliloti. Plant Physiol. 1993 Mar;101(3):819–824. doi: 10.1104/pp.101.3.819. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Gowri G., Paiva N. L., Dixon R. A. Stress responses in alfalfa (Medicago sativa L.) 12. Sequence analysis of phenylalanine ammonia-lyase (PAL) cDNA clones and appearance of PAL transcripts in elicitor-treated cell cultures and developing plants. Plant Mol Biol. 1991 Sep;17(3):415–429. doi: 10.1007/BF00040636. [DOI] [PubMed] [Google Scholar]
- Jakobek J. L., Smith J. A., Lindgren P. B. Suppression of Bean Defense Responses by Pseudomonas syringae. Plant Cell. 1993 Jan;5(1):57–63. doi: 10.1105/tpc.5.1.57. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Matern U., Heller W., Himmelspach K. Conformational changes of apigenin 7-O-(6-O-malonylglucoside), a vacuolar pigment from parsley, with solvent composition and proton concentration. Eur J Biochem. 1983 Jun 15;133(2):439–448. doi: 10.1111/j.1432-1033.1983.tb07483.x. [DOI] [PubMed] [Google Scholar]
- McKhann H. I., Hirsch A. M. Isolation of chalcone synthase and chalcone isomerase cDNAs from alfalfa (Medicago sativa L.): highest transcript levels occur in young roots and root tips. Plant Mol Biol. 1994 Mar;24(5):767–777. doi: 10.1007/BF00029858. [DOI] [PubMed] [Google Scholar]
- Meier B. M., Shaw N., Slusarenko A. J. Spatial and temporal accumulation of defense gene transcripts in bean (Phaseolus vulgaris) leaves in relation to bacteria-induced hypersensitive cell death. Mol Plant Microbe Interact. 1993 Jul-Aug;6(4):453–466. doi: 10.1094/mpmi-6-453. [DOI] [PubMed] [Google Scholar]
- Morita T., Nishibe H., Iwanaga S., Suzuki T. Studies on the activation of bovine prothrombin. Isolation and characterization of the fragments released from the prothrombin by activated factor X. J Biochem. 1974 Nov;76(5):1031–1048. [PubMed] [Google Scholar]
- Phillips D. A., Joseph C. M., Maxwell C. A. Trigonelline and Stachydrine Released from Alfalfa Seeds Activate NodD2 Protein in Rhizobium meliloti. Plant Physiol. 1992 Aug;99(4):1526–1531. doi: 10.1104/pp.99.4.1526. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Phillips D. A., Kapulnik Y. Plant isoflavonoids, pathogens and symbionts. Trends Microbiol. 1995 Feb;3(2):58–64. doi: 10.1016/s0966-842x(00)88876-9. [DOI] [PubMed] [Google Scholar]
- Reddy A. S., Jena P. K., Mukherjee S. K., Poovaiah B. W. Molecular cloning of cDNAs for auxin-induced mRNAs and developmental expression of the auxin-inducible genes. Plant Mol Biol. 1990 May;14(5):643–653. doi: 10.1007/BF00016498. [DOI] [PubMed] [Google Scholar]
- Volpin H., Elkind Y., Okon Y., Kapulnik Y. A Vesicular Arbuscular Mycorrhizal Fungus (Glomus intraradix) Induces a Defense Response in Alfalfa Roots. Plant Physiol. 1994 Feb;104(2):683–689. doi: 10.1104/pp.104.2.683. [DOI] [PMC free article] [PubMed] [Google Scholar]