Abstract
SAP11 is an effector protein that has been identified in various phytoplasma species. It localizes in the plant nucleus and can bind and destabilize TEOSINE BRANCHES/CYCLOIDEA/PROLIFERATING CELL FACTOR (TCP) transcription factors. Although SAP11 of different phytoplasma species share similar activities, their protein sequences differ greatly. Here, we demonstrate that the SAP11-like protein of ‘Candidatus Phytoplasma mali’ (‘Ca. P. mali’) strain PM19 localizes into the plant nucleus without requiring the anticipated nuclear localization sequence (NLS). We show that the protein induces crinkled leaves and siliques, and witches’ broom symptoms, in transgenic Arabidopsis thaliana (A. thaliana) plants and binds to six members of class I and all members of class II TCP transcription factors of A. thaliana in yeast two-hybrid assays. We also identified a 17 amino acid stretch previously predicted to be a nuclear localization sequence that is important for the binding of some of the TCPs, which results in a crinkled leaf and silique phenotype in transgenic A. thaliana. Moreover, we provide evidence that the SAP11-like protein has a destabilizing effect on some TCPs in vivo.
Highlights
Because our results indicate that the 40–56 amino acid stretch of AP_SAP11-like_PM19 is not responsible for nuclear localization of the protein, but responsible for some of the phenotypic characteristics of the transgenic Arabidopsis expressing AP_SAP11-like protein, we further analyzed its possible role during the interaction with AtTCP transcription factors using Y2H screens
The results clearly indicate that the 40–56 amino acid stretch is important for the interaction with some AtTCPs, those of class II
The results showed that the AP_SAP11-like_PM19∆40–56 cannot destabilize the AtTCP3 and 4 of class II compared to the wt protein (Figure 7)
Summary
The delivery of effector proteins and small molecules into the plant host is a common strategy of plant pathogens, including bacteria, fungi, oomycetes, and nematodes, to enhance the hosts’ susceptibility and benefit the pathogen’s infectiousness [1]. The function of these effectors ranges from suppression of the plant immune system to alteration of plant behavior and development [1]. Identifying targets of plant pathogen effectors and revealing plant–microbe interactions facilitate the understanding of the infection mechanisms and, allows phytoplasma diseases to be controlled
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