An everlasting pioneer: the story of Antirrhinum research

Despite the tremendous success of Arabidopsis thaliana, no single model can represent the vast range of form that is seen in the ~250,000 existing species of flowering plants (angiosperms). Here, we consider the history and future of an alternative angiosperm model — the snapdragon Antirrhinum majus. We ask what made Antirrhinum attractive to the earliest students of variation and inheritance, and how its use led to landmark advances in plant genetics and to our present understanding of plant development. Finally, we show how the wide diversity of Antirrhinum species, combined with classical and molecular genetics — the two traditional strengths of Antirrhinum — provide an opportunity for developmental, evolutionary and ecological approaches. These factors make A. majus an ideal comparative angiosperm

A conserved microtubule-binding region in Xanthomonas XopL is indispensable for induced plant cell death reactions.

Pathogenic Xanthomonas bacteria cause disease on more than 400 plant species. These Gram-negative bacteria utilize the type III secretion system to inject type III effector proteins (T3Es) directly into the plant cell cytosol where they can manipulate plant pathways to promote virulence. The host range of a given Xanthomonas species is limited, and T3E repertoires are specialized during interactions with specific plant species. Some effectors, however, are retained across most strains, such as Xanthomonas Outer Protein L (XopL). As an 'ancestral' effector, XopL contributes to the virulence of multiple xanthomonads, infecting diverse plant species. XopL homologs harbor a combination of a leucine-rich-repeat (LRR) domain and an XL-box which has E3 ligase activity. Despite similar domain structure there is evidence to suggest that XopL function has diverged, exemplified by the finding that XopLs expressed in plants often display bacterial species-dependent differences in their sub-cellular localization and plant cell death reactions. We found that XopL from X. euvesicatoria (XopLXe) directly associates with plant microtubules (MTs) and causes strong cell death in agroinfection assays in N. benthamiana. Localization of XopLXe homologs from three additional Xanthomonas species, of diverse infection strategy and plant host, revealed that the distantly related X. campestris pv. campestris harbors a XopL (XopLXcc) that fails to localize to MTs and to cause plant cell death. Comparative sequence analyses of MT-binding XopLs and XopLXcc identified a proline-rich-region (PRR)/α-helical region important for MT localization. Functional analyses of XopLXe truncations and amino acid exchanges within the PRR suggest that MT-localized XopL activity is required for plant cell death reactions. This study exemplifies how the study of a T3E within the context of a genus rather than a single species can shed light on how effector localization is linked to biochemical activity

Co‐circulation and characterization of novel African arboviruses (genus Ephemerovirus ) in cattle, Mayotte island, Indian Ocean, 2017

International audienceMayotte is an island located in the Mozambique Channel, between Mozambique and Madagascar, in the South Western Indian Ocean region. A severe syndrome of unknown aetiology has been observed seasonally since 2009 in cattle (locally named "cattle flu"), associated with anorexia, nasal discharge, hyperthermia and lameness. We sampled blood from a panel of those severely affected animals at the onset of disease signs and analysed these samples by next-generation sequencing. We first identified the presence of ephemeral bovine fever viruses (BEFV), an arbovirus belonging to the genus Ephemerovirus within the family Rhabdoviridae, thus representing the first published sequences of BEFV viruses of African origin. In addition, we also discovered and genetically characterized a potential new species within the genus Ephemerovirus, called Mavingoni virus (MVGV) from one diseased animal. Finally, both MVGV and BEFV have been identified in cattle from the same herd, evidencing a co-circulation of different ephemeroviruses on the island. The clinical, epidemiological and virological information strongly suggests that these viruses represent the etiological agents of the observed "cattle flu" within this region. This study highlights the importance of the strengthening and harmonizing arboviral surveillance in Mayotte and its neighbouring areas, including Africa mainland, given the importance of the diffusion of infectious diseases (such as BEFV) mediated by animal and human movements in the South Western Indian Ocean area

XopL_Xoo and XopL_Xac localize to MTs.

Confocal microscopy of lower epidermal cells of GFP-TUA6 stable transgenic N. benthamiana leaves. Leaves were agroinfected (OD600 of 0.4) to express synthesized (codon-optimized) (A) XopLXac and (B) XopLXoo translationally fused to a C-terminal mCherry. (A) and (B) are zoomed-out versions of cells depicted in Fig 4G and Fig 4J, respectively. mCherry-tagged XopLs are visible in magenta and the GFP channel is not shown here, ‘n’ marks the nucleus, white arrows show example MTs. Scale bars are 20 μm. Insets are magnifications of the nuclei (scale bar is 10 μm). (C) Plant reactions to codon-optimized XopLs were monitored at 6 dpi. (TIFF)</p

DMSO control infiltrations into XopL_Xe-expressing tissue did not rescue MTs.

Confocal microscopy of lower epidermal cells of GFP-TUA6 (labels MTs) stable transgenic N. benthamiana leaves. Leaves were agroinfected (OD600 of 0.4) to express (A-C) XopLXe-mCherry, (D-F) XopLm-mCherry and (K-M) mCherry which was then treated with DMSO at 4 hpi. Samples were harvested for microscopy 2 dpi. The GFP channel is visible in white (labeled MTs), the mCherry channel in magenta. Plastids are visible in cyan. Scale bars are 20 μm. (TIFF)</p

KTN1 and PHS1 destroy MTs.

Confocal microscopy of lower epidermal cells of GFP-TUA6 stable transgenic N. benthamiana leaves. Leaves were agroinfected (OD600 of 0.8) to express (A) mCherry, (B) KTN1, (C) PHS1 185-700aa (PHS185-700) or (D) PHS1 1-700aa (PHS1-700) tagged with GFP. Samples were harvested for microscopy at 2 dpi. Images show the GFP channel, where MTs (GFP-TUA6 labeled) are typically visible (i.e., panel A). Scale bars are 20 μm. (E-H) are zoomed in versions of (A-D) respectively. (I) Cell death quantification via red fluorescence scanning of agroinfected N. benthamiana leaves. Tissue co-expressing XopLXe (purple) or non-MT-binding derivatives (ex2127/130; blue and αLRR_XL; orange) together with GFP or MT-disrupting proteins KTN1 and PHS1185-700 was monitored for cell death 5 dpi. Boxes represent first to third quartiles, the median is marked by a horizontal line and whiskers show the distribution of remaining data points. Treatments that were significantly different than XopLXe+ GFP co-inoculations are marked with asterisks (* = p0.001; One Way Analysis of Variance on Ranks, Bonferroni post-hoc test). (TIFF)</p

MT association is correlated with MTs disassembly.

Linear regression comparing MT binding ability of XopLm derivatives with MT number remaining after expression of XopLXe derivatives. Each data point represents the MT association of a given E3 ligase mutant variant (graphed in Fig 5C) plotted against the MT number remaining after expression of the corresponding E3 ligase-active version (graphed in Fig 5D). Each data point is labeled with the derivative name. The line of best fit is blue, and the equation of the line is displayed in the upper right (Linear Regression, R2 = 0.762, F [1, 7] = 22.35, P = 0.002). (TIFF)</p

Clustal Omega multiple sequence alignment of select XopL homologs from the <i>Xanthomonas</i> genus.

XopL protein sequences from 24 strains were aligned. The strain of origin is listed on the left-hand side with the NCBI accession number of the XopL protein sequence. Amino acids are colored based on polarity (Geneious Prime). Acidic amino acids in red, basic in blue, and fuchsia highlights prolines. The XopLXe proline-rich region (PRR) is in gray, the alpha α region (α-helices 1, 2 and 3) in yellow, and the beginning of the LRR domain (visible as ‘LRR1’) in light pink. The sequence logo above the alignment shows sequence conservation at specific positions. (TIFF)</p

Taxol partially rescues MTs from XopL_Xe.

Confocal microscopy of lower epidermal cells of GFP-TUA6 (labels MTs) stable transgenic N. benthamiana leaves. Leaves were agroinfected (OD600 of 0.4) to express (A-C) XopLXe-mCherry, (D-F) XopLm-mCherry and (K-M) mCherry and treated with the MT stabilizing chemical taxol (solved in DMSO) at 4 hpi. Samples were harvested for microscopy 2 dpi. The GFP channel is visible in white (labeled MTs) and the mCherry channel in magenta. Plastids are in cyan; ‘n’ labels nuclei. Scale bars are 20 μm. (G), (H), (I), (J) Are magnified images from (A), (B), (D) and (E), respectively (area magnified is outline with a white box). Scale bars in (G-J) are 5 μm. Examples of MTs are labeled with white arrows. (TIFF)</p

Stable Transformation of the Xylella fastidiosa Citrus Variegated Chlorosis Strain with oriC Plasmids

Xylella fastidiosa is a gram-negative, xylem-limited bacterium affecting economically important crops (e.g., grapevine, citrus, and coffee). The citrus variegated chlorosis (CVC) strain of X. fastidiosa is the causal agent of this severe disease of citrus in Brazil and represents the first plant-pathogenic bacterium for which the genome sequence was determined. Plasmids for the CVC strain of X. fastidiosa were constructed by combining the chromosomal replication origin (oriC) of X. fastidiosa with a gene which confers resistance to kanamycin (Kan(r)). In plasmid p16KdAori, the oriC fragment comprised the dnaA gene as well as the two flanking intergenic regions, whereas in plasmid p16Kori the oriC fragment was restricted to the dnaA-dnaN intergenic region, which contains dnaA-box like sequences and AT-rich clusters. In plasmid p16K, no oriC sequence was present. In the three constructs, the promoter region of one of the two X. fastidiosa rRNA operons was used to drive the transcription of the Kan(r) gene to optimize the expression of kanamycin resistance in X. fastidiosa. Five CVC X. fastidiosa strains, including strain 9a5c, the genome sequence of which was determined, and two strains isolated from coffee, were electroporated with plasmid p16KdAori or p16Kori. Two CVC isolates, strains J1a12 and B111, yielded kanamycin-resistant transformants when electroporated with plasmid p16KdAori or p16Kori but not when electroporated with p16K. Southern blot analyses of total DNA extracted from the transformants revealed that, in all clones tested, the plasmid had integrated into the host chromosome at the promoter region of the rRNA operon by homologous recombination. To our knowledge, this is the first report of stable transformation in X. fastidiosa. Integration of oriC plasmids into the X. fastidiosa chromosome by homologous recombination holds considerable promise for functional genomics by specific gene inactivation