Localization of the fungal symbiont (Chaetothyriales) in Ipomoea carnea

Authors: PISTAN, MARIA - Universidad National Del Nordeste; GUTIERREZ, SUSANA - Universidad National Del Nordeste; SCHNITTGER, LEONHARD - Consejo Nacional De Investigaciones Científicas Y Técnicas(CONICET); Gardner, Dale; CHOLICH, LUCIANA - Instituto De Botánica Del Nordeste; GONZALEZ, ANA - Consejo Nacional De Investigaciones Científicas Y Técnicas(CONICET)

Submitted to: Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/30/2022
Publication Date: 4/8/2022
Citation: Pistan, M.E., Gutierrez, S.A., Schnittger, L., Gardner, D.R., Cholich, L.A., Gonzalez, A.M. 2022. Localization of the fungal symbiont (Chaetothyriales) in Ipomoea carnea. Botany. 100(9):729-736. https://doi.org/10.1139/cjb-2022-0033.
DOI: https://doi.org/10.1139/cjb-2022-0033

Interpretive Summary: The plant Ipomea carnea may contain the toxic compound known as swainsonine and causes toxicity in goats, sheep and cattle. Clinical signs of poisoning include weight loss, depression, ataxia, weakness, and paralysis. Swainsonine present in the plant has been shown to be produced by a fungus that lives in the plant. Herein is reported the use of imaging techniques to better understand what parts of the plant are associated with the fungus and to understand the process of fungal transmission within the plant. Both plants known to contain swainsonine and those that do not contain swainsonine were examined. Results confirm that the presence of the fungus is a prerequisite for the presence of swainsonine in Ipomoea carnea. In addition, the occurrence of fungus with the seed supports the theory that the fungus is vertically transmitted.

Technical Abstract: Plants belonging to the genera Astragalus, Oxytropis, Ipomoea, Sida,and Swainsona often contain the toxin swainsonine (SW), which causes a neurological disorder in livestock. It has been demonstrated that SW is produced by a symbiont fungus associated with these plants. In I. carnea, the fungus belongs to the ascomycetes of the order Chaetothyriales and grows ectopically on the adaxial surface of leaves. In this study, the presence of the symbiont fungus in different organs of I. carnea was investigated using imaging techniques to understand the process of endophyte transmission. In I. carnea plants with whitish mycelia on the leaf surface, SW could be detected in seeds. Inside the seeds, the mycelium was located on the surface of the cotyledons and on the inner side of the seed coat. We corroborated that the presence of this fungus is a prerequisite for the presence of SW in I. carnea. The demonstration of the localization of the fungus within the seed strongly suggested that this endophyte is vertically transmitted. Our observations verified that the SW-producing fungus in I. carnea is an endosymbiont with epibiotic behavior.