Draft genome assembly of the false spider mite.

The false spider mite Brevipalpus yothersi infests a broad host plant range and has become one of the most economically important species within the genus Brevipalpus. This phytophagous mite inflicts damage by both feeding on plants and transmitting plant viruses. Here, we report the first draft genome sequence of the false spider mite, which is also the first plant virus mite vector to be sequenced. The similar to 72 Mb genome (sequenced at 42x coverage) encodes similar to 16,000 predicted protein-coding genes

Structure-Function Analysis of the HrpB2-HrcU Interaction in the Xanthomonas citri Type III Secretion System

Bacterial type III secretion systems deliver protein virulence factors to host cells. Here we characterize the interaction between HrpB2, a small protein secreted by the Xanthomonas citri subsp. citri type III secretion system, and the cytosolic domain of the inner membrane protein HrcU, a paralog of the flagellar protein FlhB. We show that a recombinant fragment corresponding to the C-terminal cytosolic domain of HrcU produced in E. coli suffers cleavage within a conserved Asn264-Pro265-Thr266-His267 (NPTH) sequence. A recombinant HrcU cytosolic domain with N264A, P265A, T266A mutations at the cleavage site (HrcUAAAH) was not cleaved and interacted with HrpB2. Furthermore, a polypeptide corresponding to the sequence following the NPTH cleavage site also interacted with HrpB2 indicating that the site for interaction is located after the NPTH site. Non-polar deletion mutants of the hrcU and hrpB2 genes resulted in a total loss of pathogenicity in susceptible citrus plants and disease symptoms could be recovered by expression of HrpB2 and HrcU from extrachromossomal plasmids. Complementation of the ΔhrcU mutant with HrcUAAAH produced canker lesions similar to those observed when complemented with wild-type HrcU. HrpB2 secretion however, was significantly reduced in the ΔhrcU mutant complemented with HrcUAAAH, suggesting that an intact and cleavable NPTH site in HrcU is necessary for total functionally of T3SS in X. citri subsp. citri. Complementation of the ΔhrpB2 X. citri subsp. citri strain with a series of hrpB2 gene mutants revealed that the highly conserved HrpB2 C-terminus is essential for T3SS-dependent development of citrus canker symptoms in planta

Phytophagous mites transmitting plant viruses: Update and perspectives

Plant viruses can be effectively transmitted by phytophagous mites. Many species of mites, mainly criophyids and tenuipalpids, induce symptoms in infested plants that may be mistaken for viral diseases or may hide infections produced by unidentified putative viruses. The virus-mite interplay and the multitrophic interactions with their host plants are often inadequately described and require further clarifications. Advances in biotechnological methods could enable increasing identification and characterization of viruses transmitted and their potential mite vectors. This review examines the state of knowledge of mites and plant-virus interactions by summarizing the strengths and weaknesses in this research field, thus paving the way for new research directions

Identification of defence-related genes expressed in coffee and citrus during infection by Xylella fastidiosa

One of the phytosanitary problems of coffee cultivation in Brazil is Coffee Leaf Scorch (CLS) disease, caused by the phytopathogenic bacterium Xylella fastidiosa. Due to the economic importance of coffee to Brazil and the losses caused by X. fastidiosa, a cDNA library (RX1) was constructed using infected coffee stems. This library is one of the 37 coffee EST libraries constructed using different organs and tissues and biological conditions (Coffee Genome Project-CafEST). The objective of this study was to identify genes potentially involved in defence processes in response to X. fastidiosa infection by in silico analysis of the transcripts from the RX1 library as well as compare the coffee ESTs to citrus Xylella-infected ESTs. Clustering analysis of the RX1 library grouped a total of 7,501 sequences into 3,248 contigs, 19 of which were not found in the other 36 libraries. Additionally, 119 contigs were considered differentially expressed in comparison with the other libraries and according to statistical criteria. The global analysis of these contigs showed several genes involved in dehydration and photosynthesis. A total of 2,235 singlets were also obtained in the RX1 library and several of these genes are classically involved in defence processes. The comparison to a Xylella-infected citrus EST library revealed several genes similarly modulated in both species, indicating common defence mechanisms in both host plants in response to X. fastidiosa. The results obtained showed that water deprivation and response to osmotic and oxidative stress were expressed in a similar way in both coffee and citrus libraries. This is the first study to propose a common mechanism shared by citrus and coffee plants in response to the same pathogen.130452954

Transmission of Citrus leprosis virus C by Brevipalpus phoenicis (Geijskes) to Alternative Host Plants Found in Citrus Orchards

The equivalent of US$75 million is spent each year in Brazil to control Brevipalpus phoenicis, a mite vector of Citrus leprosis virus C (CiLV-C). In this study, we investigated the possibility that hedgerows and windbreaks normally found in citrus orchards could host CiLV-C. Mites confined by an adhesive barrier were reared on sweet orange fruit with leprosis symptoms then were transferred to leaves of Hibiscus rosa-sinensis, Malvaviscus arboreus, Grevilea robusta, Bixa orellana, and Citrus sinensis. Ninety days post infestation, the descendant mites were transferred to Pera sweet orange plants to verify the transmissibility of the virus back to citrus. Nonviruliferous mites which had no feeding access to diseased tissue were used as controls. Local chlorotic or necrotic spots and ringspots, symptoms of leprosis disease, appeared in most plants tested. Results generated by reverse-transcription polymerase chain reaction with primers specific for CiLV-C and by electron microscope analyses confirmed the susceptibility of these plants to CiLV-C.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Identification of defence-related genes expressed in coffee and citrus during infection by Xylella fastidiosa.

One of the phytosanitary problems of coffee cultivation in Brazil is Coffee Leaf Scorch (CLS) disease, caused by the phytopathogenic bacterium Xylella fastidiosa. Due to the economic importance of coffee to Brazil and the losses caused by X. fastidiosa, a cDNA library (RX1) was constructed using infected coffee stems. This library is one of the 37 coffee EST libraries constructed using different organs and tissues and biological conditions (Coffee Genome Project-CafEST). The objective of this study was to identify genes potentially involved in defence processes in response to X. fastidiosa infection by in silico analysis of the transcripts from the RX1 library as well as compare the coffee ESTs to citrus Xylella-infected ESTs. Clustering analysis of the RX1 library grouped a total of 7,501 sequences into 3,248 contigs, 19 of which were not found in the other 36 libraries. Additionally, 119 contigs were considered differentially expressed in comparison with the other libraries and according to statistical criteria. The global analysis of these contigs showed several genes involved in dehydration and photosynthesis. A total of 2,235 singlets were also obtained in the RX1 library and several of these genes are classically involved in defence processes. The comparison to a Xylella-infected citrus EST library revealed several genes similarly modulated in both species, indicating common defence mechanisms in both host plants in response to X. fastidiosa. The results obtained showed that water deprivation and response to osmotic and oxidative stress were expressed in a similar way in both coffee and citrus libraries. This is the first study to propose a common mechanism shared by citrus and coffee plants in response to the same pathogen

QBOL: a new EU project focusing on DNA barcoding of Quarantine organisms

International audienceIn 2009 a new three year EU funded project (QBOL) started on DNA barcoding of important plant pests. An international consortium of 20 partners (universities, research institutes, and phytosanitary organizations) from around the world, coordinated by Plant Research International (Wageningen, the Netherlands), will collect DNA barcodes from many plant pathogenic quarantine organisms, store these sequences in a database accessible over the internet, develop a DNA bank and train end-users. All these activities should help National Plant Protection Services in the correct identification and detection of plant pathogenic quarantine organism

Taxonomy of the order Mononegavirales : second update 2018

In October 2018, the order Mononegavirales was amended by the establishment of three new families and three new genera, abolishment of two genera, and creation of 28 novel species. This article presents the updated taxonomy of the order Mononegavirales as now accepted by the International Committee on Taxonomy of Viruses (ICTV)