Inhibitory Effect of Tea Saponin on Major Apple-Disease-Inducing Fungi.

Plant secondary metabolites are well known for their biological functions in defending against pathogenic microorganisms. Tea saponin (TS), one type of secondary metabolite of the tea plant (Camellia sinensis), has been shown to be a valuable botanical pesticide. However, its antifungal activity in controlling the fungi Valsa mali, Botryosphaeria dothidea, and Alternaria alternata, which induce major diseases in apple (Malus domestica), has not been determined. In this study, we first determined that TS has higher inhibitory activity than catechins against the three types of fungi. We further utilized in vitro and in vivo assays to confirm that TS showed high antifungal activity against the three types of fungi, especially for V. mali and B. dothidea. In the in vivo assay, application of a 0.5% TS solution was able to restrain the fungus-induced necrotic area in detached apple leaves efficiently. Moreover, a greenhouse infection assay also confirmed that TS treatment significantly inhibited V. mali infection in leaves of apple seedlings. In addition, TS treatment activated plant immune responses by decreasing accumulation of reactive oxygen species and promoting the activity of pathogenesis-related proteins, including chitinase and ß-1,3-glucanase. This indicated that TS might serve as a plant defense inducer to activate innate immunity to fight against fungal pathogen invasion. Therefore, our data indicated that TS might restrain fungal infection in two ways, by directly inhibiting the growth of fungi and by activating plant innate defense responses as a plant defense inducer.

Functional characterization of an apple apomixis-related MhFIE gene in reproduction development.

The products of the FIS genes play important regulatory roles in diverse developmental processes, especially in seed formation after fertilization. In this study, a FIS-class gene MhFIE was isolated from apple. It encoded a predicted protein highly similar to polycomb group (PcG) protein FERTILIZATION-INDEPENDENT ENDOSPERM (FIE). MhFIE functioned as an Arabidopsis FIE homologue, as indicated by functional complementation experiment using Arabidopsis fie mutant. In addition, BiFC assay showed that MhFIE protein interacted with AtCLF. Furthermore, transgenic Arabidopsis ectopically expressing MhFIE produced less APETALA3 (AtAP3) and AGAMOUS (AtAG) transcripts than WT control, and therefore exhibited abnormal flower, seed development. These results suggested that polycomb complex including FIE and CLF proteins played an important role in reproductive development by regulating the expression of its downstream genes. In addition, it was found that MhFIE constitutively expressed in various tissues tested. Its expression levels were lower in apomictic apple species than the sexual reproductive species, suggested it was possibly involved into apomixis in apple. Furthermore, the hybrids of tea crabapple generated MhFIE transcripts at different levels. The parthenogenesis capacity was negatively correlated with MhFIE expression level in these hybrids. These results suggested that MhFIE was involved into the regulation of flower development and apomixis in apple.