Phytoplasma effector SWP1 induces witches’ broom symptom by destabilizing the TCP transcription factor BRANCHED1

Abstract

Phytoplasmas are insect-transmitted phytopathogenic bacteria, which secrete effector proteins that are often responsible for altering the plant morphology and behaviours of their vectors. Phytoplasma multifunctional effector proteins TENGU and SAP11 induce typical witches' broom symptoms, but their mode of action remains unknown. Previously, we have identified a SAP11-like effector from wheat blue dwarf phytoplasma, SWP1, which induces witches' broom symptoms in Nicotiana benthamiana. In this study, we observed that SWP1-expressing transgenic Arabidopsis thaliana plants showed typical witches' broom symptoms. On overexpression of SWP1 truncation mutants in N. benthamiana, we identified that the coiled-coil domain and nuclear localization were responsible for the induction of witches' broom symptoms. In addition, using yeast two-hybrid and bimolecular fluorescence complementation assays, we demonstrated that SWP1 interacts with A. thaliana transcription factor TCP18 (BRC1), the key negative regulator of branching signals in various plant species. Moreover, in planta co-expression analysis showed that SWP1 promotes the degradation of BRC1 via a proteasome system. These findings suggest that the phytoplasma effector SWP1 induces witches' broom symptoms through targeting of BRC1 and promoting its degradation.

Functional variation in phyllogen, a phyllody‐inducing phytoplasma effector family, attributable to a single amino acid polymorphism

“…Although functional analyses of several effector homologs of phytoplasma have become areas of active research (Sugawara et al ., 2013; Maejima et al ., 2014; Chang et al ., 2018; Wang et al ., 2018b; Pecher et al ., 2019), the evolutionary dynamics of these homologs have not yet been addressed. In the current study, phylogenetic analyses indicated that the phyllogen family evolved independently of “ Ca .…”

“…Although functional analyses of several effector homologs of phytoplasma have become areas of active research (Sugawara et al, 2013;Maejima et al, 2014;Chang et al, 2018;Wang et al, 2018b;Pecher et al, 2019), the evolutionary dynamics of these homologs…”

The Regulation of CIN-like TCP Transcription Factors

“…TCP family transcription factors governs various key developmental processes during the life cycle of plants. TCPs regulate seed germination, leaf development, outgrowth of shoot branches, flowering, flower development, silique and ovule development, photomorphogenesis, thermomorphogenesis, circadian rhythms, defense responses and senescence [ 11 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 ]. The tight regulation of TCPs is very important for plant development and survival.…”

Inhibition of Arabidopsis thaliana CIN‐like TCP transcription factors by Agrobacterium T‐DNA‐encoded 6B proteins

“…In yeast, TE‐2‐6B, TE‐1‐6B‐L and TE‐1‐6B‐R were found to bind different subsets of TCP proteins. Differences in TCP‐binding patterns were also noted for some SAP11 variants (Chang et al , ; Wang et al , ). Strong Arabidopsis TCP phenotypes require simultaneous inactivation of several TCP genes (Efroni et al , ; Schommer et al , ; Koyama et al , ; Alvarez et al , ; Bresso et al , ).…”