Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/2/2006
Publication Date: 8/1/2006
Citation: Niemi, K., Sutela, S., Haggman, H., Scagel, C.F., Vuosku, J., Jokela, A., Sarjala, T. 2006. Changes in polyamine content and localization of ADC and ODC mRNA transcripts during mycorrhiza formation by suillus variegatus on pinus sylvestris in an in vitro cultivation system. Journal of Experimental Botany. 57(11):2795-2804.
Interpretive Summary: Understanding hormonal factors regulating root development and formation of mycorrhizae has important practical application to propagation of plants from tissue culture and cuttings. We investigated the role of fungus- and plant-produced polyamines (PAs) in root development and mycorrhizae formation on Pinus sylvestris seedlings. Inoculation with mycorrhizal fungi increased PAs in seedlings followed by mycorhizae formation. Mycorrhiza-induced PA accumulation was linked to induction of lateral root formation. Increased PA in plants was found to be a result of both PAs produced by the mycorrhizal fungus and PA-production the plant induced by the establishment of the symbiosis. The results from this work have expanded knowledge on the mechanisms involved in the regulation of root growth by determining that changes in hormones associated with increased growth can be altered by mycorrhizal fungi.
Technical Abstract: Polyamines (PAs) are N-rich growth factors implicated in symbiotic mycorrhizal interaction. We investigated PA metabolism during mycorrhizae formation between P. sylvestris seedlings and an ECM fungus Suillus variegatus (Swatz: Fr.) O. Kunze at transcriptome and metabolome levels. Inoculation with S. variegatus resulted in a significant increase in the concentrations of most free and some conjugated PAs in P. sylvestris seedlings within the first week in dual culture. This was followed by mycorrhizae formation and a dramatic increase in root growth parameters, indicating the involvement of PAs in the early interaction between the symbionts. In inoculated but not in non-inoculated roots, P. sylvestris arginine decarboxylase (ADC) mRNA transcript was localized in pericycle, the outermost layer of vascular cylinder. This indicates that PAs are involved in the induction of lateral root formation by S. variegatus. In all seedlings, ADC gene expression was localized in parenchyma cells adjacent to developing or mature tracheids; this suggests that root PAs may be translocated to the other parts of the seedling. Spermidine (Spd) concentration in the external hyphae decreased within the first week in dual culture, concomitantly with the accumulation of Spd and spermine (Spm) in the mycorrhizal root system. Accumulation of Spd and Spm, together with the detection of putrescine (Put) in the culture filtrate of S. variegatus and localization of S. variegatus ornithine decarboxylase (ODC) mRNA transcript in developing hyphal mantle and Hartig net suggest that PA translocation from the fungal partner to the host plant plays an important role in the regulation of PA metabolism in this mycorrhizal interaction.