Abstract
Ustilago esculenta, resembling a fungal endophyte in Zizania latifolia, inhibits the host plant flowering and induces the host stems to swell and form edible galls. It is well believed that when and how the fungus infects and proliferates in the host plants during the host development is of importance in the edible gall formation. Mitogen-activated protein kinases (MAPKs) have been found to play an important role in sensing environment cues and regulating infection. Two MAPK genes UeKpp2 and UeKpp6 from U. esculenta were cloned and suggested to be involved in the Fus3/Kss1 pathway by a phylogenetic analysis with the neighbor-joining method. Quantitative RT-PCR (qRT-PCR) analyses indicated that expression of UeKpp2 and UeKpp6 were induced during mating and infection processes, and their expression patterns displayed differentially under different carbon and nitrogen sources. In addition, subcellular localization of UeKpp2 or UeKpp6 fused with the reporter green fluoresce protein was observed by confocal laser scanning microscope, and yeast two-hybrid assays were carried out. Results showed that both UeKpp2 and UeKpp6 were located in cytoplasm and interacted with UePrf1, indicating their involvement in hyphal growth and host–pathogen regulation. Only UeKpp2 but not UeKpp6 interacted with the upstream MAPK kinase UeFuz7, implying an additional MAPK pathway, in which UeKpp6 involved, existed.
Highlights
Ustilago esculenta, belonging to the Ustilaginaceae of basidiomycetes, resembles an endophytic fungus of Zizania latifolia, a perennial aquatic grass widely cultivated in southeastern Asian countries [1]
The expression pattern of UeKpp2 to the arginine and N H4NO3 treatments indicated its role in mating in vitro, because of its up-regulation in the MT type strains with promoted hyphal growth and down-regulation in the T type strains with inhibited hyphal growth (Fig. 3a, b)
UeKpp6 might have an undiscovered role in the nitrogen response because in the methionine and NH4NO3 treatments, the expression of UeKpp6 was up-regulated in the T type strains with inhibited hyphal growth but down-regulated in the MT type strains with promoted hyphal growth (Fig. 3a, c), which is opposite to the predicted mating regulation roles
Summary
Ustilago esculenta, belonging to the Ustilaginaceae of basidiomycetes, resembles an endophytic fungus of Zizania latifolia, a perennial aquatic grass widely cultivated in southeastern Asian countries [1]. The U. esculenta-infected host plants, commonly called jiaobai in China, fail to flower and produce seeds, whereas the plant upper stems swell and form edible galls. The majority of swollen galls with white appearance and soft tissues, named white jiaobai, are consumed as an aquatic vegetable for its flavor and delicacy [2]. Galls filled with dark-colored teliospores, called grey jiaobai, always appear in a harvest season [3]. Yafen Zhang and Qianwen Ge contributed to this work.
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