Wheat blue dwarf (WBD) is one of the most economically damaging cereal crop diseases in northwestern PR China. The agent associated with the WBD disease is a phytoplasma affiliated with the aster ...yellows (AY) group, subgroup C (16SrI-C). Since phytoplasma strains within the AY group are ecologically and genetically diverse, it has been conceived that the AY phytoplasma group may consist of more than one species. This communication presents evidence to demonstrate that, while each of the two 16 rRNA genes of the WBD phytoplasma shares >97.5 % sequence similarity with that of the '
Phytoplasma asteris' reference strain, the WBD phytoplasma clearly represents an ecologically separated lineage: the WBD phytoplasma not only has its unique transmitting vector (
) but also elicits a distinctive symptom in its predominant plant host (wheat). In addition, the WBD phytoplasma possesses molecular characteristics that further manifest its significant divergence from '
. P. asteris'. Such molecular characteristics include lineage-specific antigenic membrane proteins and a lower than 95 % genome-wide average nucleotide identity score with '
. P. asteris'. These ecological, molecular and genomic evidences justify the recognition of the WBD phytoplasma as a novel taxon, '
Phytoplasma tritici'.
Phytoplasmas are insect-transmitted phytopathogenic bacteria that can alter plant morphology and the longevity and reproduction rates and behavior of their insect vectors. There are various examples ...of animal and plant parasites that alter the host phenotype to attract insect vectors, but it is unclear how these parasites accomplish this. We hypothesized that phytoplasmas produce effectors that modulate specific targets in their hosts leading to the changes in plant development and insect performance. Previously, we sequenced and mined the genome of Aster Yellows phytoplasma strain Witches’ Broom (AY-WB) and identified 56 candidate effectors. Here, we report that the secreted AY-WB protein 11 (SAP11) effector modulates plant defense responses to the advantage of the AY-WB insect vector Macrosteles quadrilineatus. SAP11 binds and destabilizes Arabidopsis CINCINNATA (CIN)-related TEOSINTE BRANCHED1, CYCLOIDEA, PROLIFERATING CELL FACTORS 1 and 2 (TCP) transcription factors, which control plant development and promote the expression of lipoxygenase (LOX) genes involved in jasmonate (JA) synthesis. Both the Arabidopsis SAP11 lines and AY-WB–infected plants produce less JA on wounding. Furthermore, the AY-WB insect vector produces more offspring on AY-WB–infected plants, SAP11 transgenic lines, and plants impaired in CIN-TCP and JA synthesis. Thus, SAP11-mediated destabilization of CIN-TCPs leads to the down-regulation of LOX2 expression and JA synthesis and an increase in M. quadrilineatus progeny. Phytoplasmas are obligate inhabitants of their plant host and insect vectors, in which the latter transmits AY-WB to a diverse range of plant species. This finding demonstrates that pathogen effectors can reach beyond the pathogen–host interface to modulate a third organism in the biological interaction.
Phytoplasma symptoms, including proliferation, witches’ broom, leaf rolling and yellowing, were observed in jujube (Ziziphus jujube) nurseries in the East of Iran. Total nucleic acid was extracted ...from symptomatic and symptomless plants, and was tested for phytoplasma presence using nested PCR. Amplicons of about 1.8 kb (primer pair P1/P7) and 1.25 kb (R16F2n/R16R2) were obtained from all symptomatic plants but not from symptomless plants. Restriction fragment length polymorphism (RFLP) analysis of R16F2n/R2 amplicons using KpnI, HaeIII, RsaI, AluI, HpaII, HhaI, TaqI, MseI, BfaI and ThaI restriction enzymes showed two RFLP patterns referable to 16SrI and 16SrVI phytoplasma groups. The consensus sequences of Z. jujube yellowing and witches’ broom of six samples correspond to ‘Candidatus Phytoplasma asteris’ and ‘Candidatus Phytoplasma trifolii’-related strains. Two R16F2n/R16R2 16S rDNA sequences representative of each RFLP profile, one each from witches’ broom (accession number MK379605) and yellowing (MK379604) host symptoms, were submitted to the GenBank. Phylogenetic analysis confirmed that the phytoplasma strains associated with jujube yellowing clustered within the 16SrI phytoplasma clade, and those associated with witches’ broom clustered within the 16SrVI clade. Restriction analysis confirmed that virtual RFLP patterns of the jujube yellowing and witches’ broom phytoplasma strains were identical to the reference pattern of 16SrI-B and 16SrVI-A. This is the first report of these phytoplasma strains associations with witches’ broom and yellowing in jujube plants.
“
Candidatus
Phytoplasma australiense” is associated with floral malformations in sesame but the interaction remains largely unexplored. A label-free quantitative shotgun proteomics approach through ...liquid chromatography-mass spectrometry quadruple time-of-flight was used to analyze changes in the proteome of asymptomatic (control) and symptomatic (phytoplasma-infected) sesame plants to identify proteins differentially expressed during phytoplasma infection at early stages of flower development. A total of 3457 and 1704 proteins were identified from asymptomatic and symptomatic samples respectively through proteome profiling with three runs per sample. Several differentially abundant proteins (DAPs) were identified which might be involved in sesame-phytoplasma interaction. The DAPs identified were related to transcription, cell division, chromosome partitioning, defense mechanisms, negative regulation of flower development, amino acid transport and metabolism, signal transduction and RNA processing, and its modifications. Of these proteins, 21 were downregulated while 212 were significantly upregulated in symptomatic sesame plants compared to the control plants. The floral development-related proteins like UBP16 and DCAF1 were found to be downregulated while negative regulators/repressors of floral development genes, HUA2, PIE1, and ICU2, were upregulated in symptomatic samples indicating phytoplasma’s role in altering the expression of these genes. Validation of these genes through quantitative retro-transcripted PCR suggested that the DAPs observed in symptomatic sesame might be induced by phytoplasma presence to suppress flowering via negative regulation of flower development.
Graphical abstract
Specific scope
This Standard describes a diagnostic protocol for ‘Candidatus Phytoplasma phoenicium’.
This Standard should be used in conjunction with PM 7/76 Use of EPPO diagnostic protocols.
1
...Specific approval and amendment
Approved in 2021–06.
In Australia,
little leaf (StLL) phytoplasma has been detected in
Vogel,
Krapov,
L.,
L.,
L., and
L. The 16S rRNA gene sequence of StLL phytoplasma strains from
,
and
were compared and share 99.93-100 ...% nucleotide sequence identity. Phylogenetic comparisons between the 16S rRNA genes of StLL phytoplasma and other '
Phytoplasma' species indicate that StLL represents a distinct phytoplasma lineage. It shares its most recent known ancestry with '
. Phytoplasma luffae' (16SrVIII-A), with which it has 97.17-97.25 % nucleotide identity.
RFLP analysis of the 16S rRNA amplicon using
PhyClassifier indicate that StLL phytoplasmas have a unique pattern (similarity coefficient below 0.85) that is most similar to that of
. Phytoplasma luffae'. The unique
RFLP patterns were confirmed
. Nucleotide sequences of genes that are more variable than the 16S rRNA gene, namely
(tu-elongation factor),
(partial translocation gene), and the partial
(
) gene operon (
), produced phylogenetic trees with similar branching patterns to the 16S rRNA gene tree. Sequence comparisons between the StLL 16S rRNA spacer region confirmed previous reports of
interoperon sequence heterogeneity for StLL, where the spacer region of
encodes a complete tRNA-Isoleucine gene and the
region does not. Together these results suggest that the Australian phytoplasma, StLL, is unique according to the International Organization for Mycoplasmology (IRPCM) recommendations. The novel taxon '
. Phytoplasma stylosanthis' is proposed, with the most recent strain from a potato crop in Victoria, Australia, serving as the reference strain (deposited in the Victorian Plant Pathology Herbarium as VPRI 43683).
Phytoplasmas are insect-borne bacterial pathogens capable of secreting effectors into host cells and interfering with host plant defense response processes. Previous studies have found that the ...Candidatus Phytoplasma tritici effector SWP12 binds to and destabilizes the wheat transcription factor TaWRKY74, increasing wheat susceptibility to phytoplasmas. Here, we used a Nicotiana benthamiana transient expression system to identify two key functional sites of SWP12 and screened a series of truncated mutants and amino acid substitution mutants to determine whether they inhibit Bax-induced cell death. Using a subcellular localization assay and online structure analysis websites, we found that structure rather than intracellular localization probably affects the function of SWP12. D33A and P85H are two inactive substitution mutants, neither of which interacts with TaWRKY74, and P85H does not inhibit Bax-induced cell death, suppress flg22-triggered reactive oxygen species (ROS) bursts, degrade TaWRKY74, or promote phytoplasma accumulation. D33A can weakly suppress Bax-induced cell death and flg22-triggered ROS bursts and degrade a portion of TaWRKY74 and weakly promote phytoplasma accumulation. S53L, CPP, and EPWB are three SWP12 homolog proteins from other phytoplasmas. Sequence analysis revealed that D33 was conserved in these proteins, and they exhibited the same polarity at P85. Transient expression in N. benthamiana showed that these proteins could inhibit Bax-induced cell death and suppress ROS bursts. Our findings clarified that P85 and D33 of SWP12 play critical and minor roles, respectively, in suppressing the plant defense response and that they play a preliminary role in determining the functions of homologous proteins.
Symptoms of decline, leaf yellowing and reddening, little leaf and malformation were observed in apricot, guava, lychee, mango, pomegranate and grapevine in fruit orchards belonging to three states ...of India namely Delhi, Maharashtra and Jammu & Kashmir during 2016–2017. Phytoplasmas belonging to three different groups were detected in all the symptomatic fruit tree samples in polymerase chain reaction with phytoplasma specific primer pairs amplifying 16S rRNA and
sec
A genes. Pair wise sequence comparison and phylogenetic analysis confirmed the presence of phytoplasmas. A ‘
Candidatus
Phytoplasma asteris’ - related strain was detected in apricot showing decline symptoms in Siot (Jammu & Kashmir). ‘
Ca
. P. australasia’ - related strain was identified in guava, lychee, mango and pomegranate in Rajbag, Sunjwan (Jammu & Kashmir), Pusa (Delhi) and Baramati (Maharashtra), respectively, exhibiting little leaf, leaf yellows and malformation symptoms. Furthermore, a rice yellow dwarf group (16SrXI-B) - related strain was detected in pomegranate and grapevine that showed leaf yellowing and reddening at Pusa (Delhi) and Baramati (Maharashtra), respectively. Subgroup analysis using virtual RFLP of 16S rDNA sequences allowed enclosing these phytoplasma strains into 16SrI-B, 16SrII-D and 16SrXI-B subgroups. In the study, identification of phytoplasma subgroups, 16SrI-B in apricot, 16SrII-D in guava, lychee, mango and pomegranate (Pusa) and 16SrXI-B in pomegranate (Baramati) and grapevine, are the first records globally.
Phytoplasmas reside exclusively in sieve tubes, tubular arrays of sieve element-companion cell complexes. Hence, the cell biology of sieve elements may reveal (ultra)structural and functional ...conditions that are of significance for survival, propagation, colonization, and effector spread of phytoplasmas. Electron microscopic images suggest that sieve elements offer facilities for mobile and stationary stages in phytoplasma movement. Stationary stages may enable phytoplasmas to interact closely with diverse sieve element compartments. The unique, reduced sieve element outfit requires permanent support by companion cells. This notion implies a future focus on the molecular biology of companion cells to understand the sieve element-phytoplasma inter-relationship. Supply of macromolecules by companion cells is channelled via specialized symplasmic connections. Ca2+-mediated gating of symplasmic corridors is decisive for the communication within and beyond the sieve element-companion cell complex and for the dissemination of phytoplasma effectors. Thus, Ca2+ homeostasis, which affects sieve element Ca2+ signatures and induces a range of modifications, is a key issue during phytoplasma infection. The exceptional physical and chemical environment in sieve elements seems an essential, though not the only factor for phytoplasma survival.
Digital PCR-based methods, such as droplet digital PCR, are one of the best tools for determination of absolute nucleic-acid copy numbers. These techniques avoid the need for reference materials with ...known target concentrations. Compared to real-time PCR, they provide higher accuracy of quantification at low target concentrations, and have higher resilience to inhibitors. In this Chapter, we describe the droplet digital PCR workflow for the detection and quantification of flavescence dorée phytoplasma.
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