Production and role of hormones during interaction of Fusarium species with maize (Zea mays L.) seedlings

Authors: VRABKA, J - Palacky University; NIEHAUS, E - Wilhelms University; MUNSTERKOTTER, M - University Of Hungary; Proctor, Robert; Brown, Daren; NOVAK, O - Palacky University; PENCIK, A - Palacky University; TARKOWSKA, D - Palacky University; HROMADOVA, K - Palacky University; HRADILOVA, M - Palacky University

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/12/2018
Publication Date: 1/11/2019
Citation: Vrabka, J., Niehaus, E.-M., Munsterkotter, M., Proctor, R.H., Brown, D.W., Novak, O., Pencik, A., Tarkowska, D., Hromadova, K., Hradilova, M. 2019. Production and role of hormones during interaction of Fusarium species with maize (Zea mays L.) seedlings. Frontiers in Plant Science. https://doi.org/10.3389/fpls.2018.01936.
DOI: https://doi.org/10.3389/fpls.2018.01936

Interpretive Summary: Optimal growth and development of crops is largely controlled by ratios of three plant hormones: auxins, cytokinins, and gibberellins. Imbalances in the ratios can negatively impact many aspects of plant health, including susceptibility to disease, flower and seed development, and yield. The fungus Fusarium is a significant threat to agriculture because it can cause disease in many crops and it can contaminate crops with toxins that are hazardous to the health of humans and domestic animals. Some Fusarium species can also produce auxins, cytokinins, and/or gibberellins. In the current study, we examined expression of plant hormone biosynthetic genes and hormone production in five closely related species of Fusarium in infected plant tissue. Production of gibberellins by Fusarium suppressed gibberellin production in the plants, whereas production of auxins resulted in higher levels of auxins in infected plants. Even though all the Fusarium species examined have the genes necessary for cytokinin production, they did not produce cytokinins in the infected plant tissue. Instead, they induced plants to produce higher levels of cytokinins. The increased production of cytokinins induced by Fusarium mangiferae in mango tissue is likely the cause of mango malformation disease, which severely reduces growth of mango trees and reduces yield of fruit. This research provides knowledge on how Fusarium species can manipulate hormone levels in crops to incite disease and negatively impact growth and yield. This knowledge will be of use to plant pathologists, plant breeders, and other scientists working to develop methods to control plant diseases and toxin contamination problems caused by Fusarium.

Technical Abstract: It has long been known that hormones affect the interaction of a phytopathogen with its host plant. The pathogen can cause changes in plant hormone homeostasis directly by affecting biosynthesis or metabolism in the plant or by synthesizing and secreting the hormone itself. We previously demonstrated that pathogenic fungi of the Fusarium species complex are able to produce three major types of hormones: auxins, cytokinins, and gibberellins. In this work, we explore changes in the levels of these hormones in maize and mango plant tissues infected with Fusarium. The ability to produce individual phytohormones varies significantly across Fusarium species and such differences likely impact host specificity inducing the unique responses noted in planta during infection. For example, the production of gibberellins by F. fujikuroi leads to elongated rice stalks and the suppression of gibberellin biosynthesis in plant tissue. Although all Fusarium species are able to synthesize auxin, sometimes by multiple pathways, the ratio of its free form and conjugates in infected tissue is affected more than the total amount produced. The recently characterized unique pathway for cytokinin de novo synthesis in Fusarium appears silenced or non-functional in all studied species during plant infection. Despite this, a large increase in cytokinin levels was detected in F. mangiferae infected plants, caused likely by the up-regulation of plant genes responsible for their biosynthesis. Thus, the accumulation of active cytokinins may contribute to mango malformation of the reproductive organs upon infection of mango trees. Together, our findings provide insight into the complex role fungal and plant derived hormones play in the fungal–plant interactions.