tale -Based Genetic Diversity of Chinese Isolates of the Citrus Canker Pathogen Xanthomonas citri subsp. citri

Summary Xanthomonas citri ssp. citri , a polar flagellated bacterium, causes citrus canker disease worldwide. In this study, we found that the X. citri ssp. citri response regulator VemR plays a regulatory role in flagellum‐derived cell motility. Deletion of the vemR gene resulted in a reduction in cell motility, as well as reductions in virulence and exopolysaccharide production. Reverse transcription‐polymerase chain reaction (RT‐PCR) demonstrated that vemR is transcribed in an operon together with rpoN2 and fleQ. In the vemR mutant, the flagellar distal rod gene flgG was significantly down‐regulated. Because flgG is also rpoN2 dependent, we speculated that VemR and RpoN2 physically interact, which was confirmed by yeast two‐hybrid and maltose‐binding protein (MBP) pull‐down assays. This suggested that the transcription of flgG is synergistically controlled by VemR and RpoN2. To confirm this, we constructed a vemR and rpoN2 double mutant. In this mutant, the reductions in cell motility and flgG transcription were unable to be restored by the expression of either vemR or rpoN2 alone. In contrast, the expression of both vemR and rpoN2 together in the double mutant restored the wild‐type phenotype. Together, our data demonstrate that the response regulator VemR functions as an RpoN2 cognate activator to positively regulate the transcription of the rod gene flgG in X. citri ssp. citri.

Section: Methodsmentioning

confidence: 97%

Response regulator VemR regulates the transcription of flagellar rod gene flgG by interacting with σ⁵⁴ factor RpoN2 in Xanthomonas citri ssp. citri

Zhao

Luo

et al. 2018

“…Low genetic variability was observed for strains isolated in the northern part of the country, but more diversity was present in the strains isolated in the southern part, where the disease was more prevalent (Jaciani et al, 2012). In China, several Xcc strains from nine citrus-growing regions were characterized and compared for the variability of TALEs (Ye et al, 2013). The result of the analysis of 105 strains with differential pathogenicity on a set of citrus hosts showed that the strains varied in the number of TALEs, ranging from three to five pthA genes (Ye et al, 2013).…”

Section: Xanthomonad Pathogenomementioning

confidence: 99%

Recent advances in the understanding of Xanthomonas citri ssp. citri pathogenesis and citrus canker disease management

Ference

Gochez²,

Behlau

et al. 2018

130

104

Taxonomic status: Bacteria; Phylum Proteobacteria; Class Gammaproteobacteria; Order Xanthomonadales; Family Xanthomonadaceae; Genus Xanthomonas; Species Xanthomonas citri ssp. citri (Xcc). Host range: Compatible hosts vary in their susceptibility to citrus canker (CC), with grapefruit, lime and lemon being the most susceptible, sweet orange being moderately susceptible, and kumquat and calamondin being amongst the least susceptible. Microbiological properties: Xcc is a rod-shaped (1.5-2.0 × 0.5-0.75 µm), Gram-negative, aerobic bacterium with a single polar flagellum. The bacterium forms yellow colonies on culture media as a result of the production of xanthomonadin. Distribution: Present in South America, the British Virgin Islands, Africa, the Middle East, India, Asia and the South Pacific islands. Localized incidence in the USA, Argentina, Brazil, Bolivia, Uruguay, Senegal, Mali, Burkina Faso, Tanzania, Iran, Saudi Arabia, Yemen and Bangladesh. Widespread throughout Paraguay, Comoros, China, Japan, Malaysia and Vietnam. Eradicated from South Africa, Australia and New Zealand. Absent from Europe.

“…Previous reports have shown a great variability in the size of the pthA genes from different X. citri strains (Al‐Saadi et al ., ; Gochez et al ., ; Lee et al ., ; Ye et al ., ). Given the mode of action of these TALE proteins, it is expected that this variability will contribute to explain differences in pathogenicity among the strains.…”

Section: Resultsmentioning

confidence: 97%

“…The existence of the pthA4 AT gene is perhaps just an accident, a by‐product of a recombination event in the course of effector evolution. Interestingly, Ye and colleagues () showed that two further strains of X. citri (029‐2 and 049) with attenuated virulence and reduced bacterial growth in planta were characterized by the absence of the 3.4‐kb band characteristic of the pthA4 gene, and by the appearance of a smaller band of around 2.4 kb, in a similar way to X. citri A T (Fig. ).…”

Section: Discussionmentioning

confidence: 96%

“…The screening of X. citri diversity in different citrus‐growing regions has identified TALEs ranking from 6.5 to 29 repeats, which likely contain different RVDs. It is suggested that the diversification is driven by recombination, facilitated by the repetitive structure of the central region, leading to variants differing in the number of repeats (Al‐Saadi et al ., ; Gochez et al ., ; Lee et al ., ; Shiotani et al ., ; Ye et al ., ). It has been demonstrated that TALEs shorter than 6.5 repeats are non‐functional in terms of gene activation; these just could be by‐products of recombination events (Boch et al , ).…”

Section: Introductionmentioning

confidence: 97%

See 1 more Smart Citation

PthA4^AT, a 7.5‐repeats transcription activator‐like (TAL) effector fromXanthomonas citrissp.citri, triggers citrus canker resistance

Roeschlin

Uviedo

García

et al. 2019

Summary Transcription activator‐like effectors (TALEs) are important effectors of Xanthomonas spp. that manipulate the transcriptome of the host plant, conferring susceptibility or resistance to bacterial infection. Xanthomonas citri ssp. citri variant AT (X. citri AT) triggers a host‐specific hypersensitive response (HR) that suppresses citrus canker development. However, the bacterial effector that elicits this process is unknown. In this study, we show that a 7.5‐repeat TALE is responsible for triggering the HR. PthA4AT was identified within the pthA repertoire of X. citri AT followed by assay of the effects on different hosts. The mode of action of PthA4AT was characterized using protein‐binding microarrays and testing the effects of deletion of the nuclear localization signals and activation domain on plant responses. PthA4AT is able to bind DNA and activate transcription in an effector binding element‐dependent manner. Moreover, HR requires PthA4AT nuclear localization, suggesting the activation of executor resistance (R) genes in host and non‐host plants. This is the first case where a TALE of unusually short length performs a biological function by means of its repeat domain, indicating that the action of these effectors to reprogramme the host transcriptome following nuclear localization is not limited to ‘classical’ TALEs.