Inhibition of polyamine oxidase activity affects tumor development during the maize-Ustilago maydis interaction

Ustilago maydis is a biotrophic plant pathogenic fungus that leads to tumor development in the aerial tissues of its host, Zea mays. These tumors are the result of cell hypertrophy and hyperplasia, and are accompanied by the reprograming of primary and secondary metabolism of infected plants. Up to now, little is known regarding key plant actors and their role in tumor development during the interaction with U. maydis. Polyamines are small aliphatic amines that regulate plant growth, development and stress responses. In a previous study, we found substantial increases of polyamine levels in tumors. In the present work, we describe the maize polyamine oxidase (PAO) gene family, its contribution to hydrogen peroxide (H2O2) production and its possible role in tumor development induced by U. maydis. Histochemical analysis revealed that chlorotic lesions and maize tumors induced by U. maydis accumulate H2O2 to significant levels. Maize plants inoculated with U. maydis and treated with the PAO inhibitor 1,8-diaminooctane exhibit a notable reduction of H2O2 accumulation in infected tissues and a significant drop in PAO activity. This treatment also reduced disease symptoms in infected plants. Finally, among six maize PAO genes only the ZmPAO1, which encodes an extracellular enzyme, is up-regulated in tumors. Our data suggest that H2O2 produced through PA catabolism by ZmPAO1 plays an important role in tumor development during the maize-U. maydis interaction.

Initiation of spontaneous tumors in radish (Raphanus sativus): Cellular, molecular and physiological events

In plant meristems, the balance of cell proliferation and differentiation is maintained by phytohormones, specifically auxin and cytokinin, as well as transcription factors. Changing of the cytokinin/auxin balance in plants may lead to developmental abnormalities, and in particular, to the formation of tumors. The examples of spontaneous tumor formation in plants include tumors formed on the roots of radish (Raphanus sativus) inbred lines. Previously, it was found that the cytokinin/auxin ratio is altered in radish tumors. In this study, a detailed histological analysis of spontaneous radish tumors was performed, revealing a possible mechanism of tumor formation, namely abnormal cambial activity. The analysis of cell proliferation patterns revealed meristematic foci in radish tumors. By using a fusion of an auxin-responsive promoter (DR5) and a reporter gene, the involvement of auxin in developmental processes in tumors was shown. In addition, the expression of the root meristem-specific WUSCHEL-related homeobox 5 (WOX5) gene was observed in cells adjacent to meristematic foci. Taken together, the results of the present study show that tumor tissues share some characteristics with root apical meristems, including the presence of auxin-response maxima in meristematic foci with adjacent cells expressing WOX5.