Submitted to: Plant Physiology and Biochemistry
Publication Type: Other
Publication Acceptance Date: 10/30/2004
Publication Date: 12/21/2004
Citation: Lozovaya, V.V., Lygin, A.V., Zernova, O.V., Li, S., Hartman, G.L., Widholm, J.M. 2004. Isoflavonoid Accumulation In Soybean Hairy Roots Upon Treatment With Fusarium Solani. Plant Physiology and Biochemistry. 42:671-679. Interpretive Summary: Many fungal pathogens reside in the soil and infect roots of important crop plants. However, studies of the plantpathogen interactions have mainly concentrated on the above ground biochemical activities and much less is known about root responses. This is in part due to the difficulty of working with roots and root pathogens. Plant roots can be cultured in the laboratory and these root cultures can simplify the study of the root-specific response during rootpathogen interactions. This system allows normal root growth that can be visually monitored. Root pathogens can be placed on roots to allow infection progression. The analyses of metabolite composition and levels could be done both in the root tissues and the culture medium. The cultured root system was used to characterize the root biosynthetic activities that might have protective functions against a soilborne fungal pathogen called Furarium solani (FS). Our results indicate that the rapid accumulation of high levels of a biochemical compound, phytoalexin glyceollin, in root tissues and culture medium could be critical for providing partial resistance in soybean against FS. This study is of interest to pathologists, plant biochemists, and other scientists that are working on host resistance to develop model systems to evaluate the host-pathogen interactions.
Technical Abstract: Hairy roots were initiated from two soybean [Glycine max (L.) Merr.]genotypes with different susceptibility (susceptible 'Spencer' and partially resistant 'PI567.374') to the disease sudden death syndrome (SDS) caused by the soil-borne fungal pathogen Fusarium solani f. sp. glycines (FSG) to study the role of isoflavonoids in the plant response to FSG infection. Hairy root cultures obtained by transformation with Agrobacterium rhizogenes allows normal root growth that can be visually monitored. The principal isoflavones (genistin, daidzin, glycitin and their malonyl conjugates and aglycones) and also isoflavonoid phytoalexins (coumestrol and glyceollin) were measured by HPLC in extracts of the FSG-inoculated and non-inoculated hairy roots. FSG mycelia grew more slowly on inoculated PI567.374 hairy roots than on Spencer hairy roots. The glyceollin content was higher in FSG-inoculated PI567.374 hairy roots than in Spencer hairy roots even though the glyceollin precursor, the isoflavone daidzein, was higher in Spencer. The de novo synthesis of isoflavones and glyceollin was confirmed by[14C]Phe incorporation into glyceollin, which was higher both in the FSG-inoculated roots and surrounding medium of the cv. PI567.374 than that of Spencer. Glyceollin was the most inhibitory to FSG growth among eight isoflavonoids tested. The levels of coumestrol, a putative phytoalexin, did not change upon FSG inoculation. The defense response was also elicited by FSG culture filtrates in hairy roots grown in liquid culture. The data obtained indicate that the ability of soybean roots to rapidly produce sufficient amounts of glyceollin in response to FSG infection might be important in providing partial resistance to this fungus.