Ectopic growth of the Chaetothyriales fungal symbiont on Ipomoea carnea

Authors: NOOR, AZIZA - New Mexico State University; NAVA, AMY - New Mexico State University; NEYAZ, MARWAH - New Mexico State University; COOKE, PETER - New Mexico State University; CREAMER, REBECCA - New Mexico State University; Cook, Daniel

Submitted to: Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/20/2021
Publication Date: 10/1/2021
Citation: Noor, A.I., Nava, A., Neyaz, M., Cooke, P., Creamer, R., Cook, D. 2021. Ectopic growth of the Chaetothyriales fungal symbiont on Ipomoea carnea. Botany. 99(10):619-627. https://doi.org/10.1139/cjb-2021-0037.
DOI: https://doi.org/10.1139/cjb-2021-0037

Interpretive Summary: Swainsonine, an indolizidine alkaloid, is an alpha-mannosidase and mannosidase II inhibitor that alters glycoprotein processing and causes lysosomal storage disease. Swainsonine is the toxic principle in several plant species worldwide and causes severe toxicosis in livestock grazing these plants. Swainsonine occurs sporadically in three diverse plant families: the Convolvulaceae, Fabaceae, and Malvaceae. All swainsonine-containing plant taxa investigated to date are associated with fungal symbionts that produce swainsonine. Alternaria section Undifilum associated symbionts within Astragalus and Oxytropis species are non-pathogenic to the host plant and are thought to be commensalistic or mutualistic. Microscopic evidence suggests that Alternaria section Undifilum mycelia grow endophytically as a highly branched network, pervading the intercellular spaces of the host plant without causing an obvious response in the neighboring plant tissues. Among the swainsonine-containing Convolvulaceous species, the bush morning glory, Ipomoea carnea is associated with a symbiont belonging to the Chaetothyriales. Macroscopic and microscopic data reported here demonstrate that the Chaetothyriales symbiont associated with I. carnea grows ectopically on the adaxial surface of leaves as a lacy-mycelia in plants that contain swainsonine and was not present on plants lacking swainsonine that were derived from fungicide treated seeds. Hyphae were not observed on the surface of any other tissues including the abaxial leaf surface, petiole, and stem. Mycelia were not visible in internal tissues below the epidermis and there did not appear to be any hyphal extensions within the fibrovascular bundles or stomata. Longitudinal and/or cross sections of the stems or petioles did not show evidence of hyphae growing between cells. These results suggest an epibiotic growth habit of the Chaetothyriales symbiont in association with I. carnea.

Technical Abstract: Swainsonine, an indolizidine alkaloid, is an alpha-mannosidase and mannosidase II inhibitor that alters glycoprotein processing and causes lysosomal storage disease. Swainsonine is the toxic principle in several plant species worldwide and causes severe toxicosis in livestock grazing these plants. Swainsonine occurs sporadically in three diverse plant families: the Convolvulaceae, Fabaceae, and Malvaceae. All swainsonine-containing plant taxa investigated to date are associated with fungal symbionts that produce swainsonine. Alternaria section Undifilum associated symbionts within Astragalus and Oxytropis species are non-pathogenic to the host plant and are thought to be commensalistic or mutualistic. Microscopic evidence suggests that Alternaria section Undifilum mycelia grow endophytically as a highly branched network, pervading the intercellular spaces of the host plant without causing an obvious response in the neighboring plant tissues. Among the swainsonine-containing Convolvulaceous species, the bush morning glory, Ipomoea carnea is associated with a symbiont belonging to the Chaetothyriales. Macroscopic and microscopic data reported here demonstrate that the Chaetothyriales symbiont associated with I. carnea grows ectopically on the adaxial surface of leaves as a lacy-mycelia in plants that contain swainsonine and was not present on plants lacking swainsonine that were derived from fungicide treated seeds. Hyphae were not observed on the surface of any other tissues including the abaxial leaf surface, petiole, and stem. Mycelia were not visible in internal tissues below the epidermis and there did not appear to be any hyphal extensions within the fibrovascular bundles or stomata. Longitudinal and/or cross sections of the stems or petioles did not show evidence of hyphae growing between cells. These results suggest an epibiotic growth habit of the Chaetothyriales symbiont in association with I. carnea.