Endophytes and Plant Extracts as Potential Antimicrobial Agents against Liberibacter Asiaticus, Causal Agent of Huanglongbing.

Huanglongbing (HLB), also known as citrus greening, is an insidious disease in citrus and has become a threat to the sustainability of the citrus industry worldwide. In the U.S.

Sensory quality of Citrus scion hybrids with Poncirus trifoliata in their pedigrees.

Hybrids of Poncirus trifoliata L. Raf. with Citrus have shown degrees of tolerance to the deadly citrus greening disease, hence prompting interest as potential commercial varieties.

Two Liberibacter Proteins Combine to Suppress Critical Innate Immune Defenses in Citrus.

We adopted a systems-based approach to determine the role of two Liberibacter asiaticus (Las) proteins, and Effector 3, in Huanglongbing (HLB) pathogenesis. While a published work suggests the involvement of these Las proteins HLB pathogenesis, the exact structure-based mechanism of their action has not been elucidated. We conducted the following experiments to determine the structure-based mechanisms of action.

Rationale for reconsidering current regulations restricting use of hybrids in orange juice.

Huanglongbing (HLB) is a disease that has devastated the Florida citrus industry, threatens the entire U.S. citrus industry, and globally is rapidly spreading.

An in vitro protocol for rapidly assessing the effects of antimicrobial compounds on the unculturable bacterial plant pathogen, Liberibacter asiaticus.

Background: Most bacteria are not culturable, but can be identified through molecular methods such as metagenomics studies. Due to specific metabolic requirements and symbiotic relationships, these bacteria cannot survive on typical laboratory media. Many economically and medically important bacteria are unculturable; including phloem-limited plant pathogens like Liberibacter asiaticus (CLas).

Hexaacetyl-chitohexaose, a chitin-derived oligosaccharide, transiently activates citrus defenses and alters the feeding behavior of Asian citrus psyllid.

Plants have a perception system triggered by pathogen and pest signals to initiate defense. These signals include evolutionarily conserved molecules from microbes and insects termed pathogen/herbivore-associated molecular patterns (PAMPs/HAMPs). Here we showed that hexaacetyl-chitohexaose (HC), an oligosaccharide from chitin, a structural component in insect exoskeletons and fungi cell walls, upregulated defense-associated genes , , , , and , and downregulated at 1 h after HC treatment in Sun Chu Sha mandarin leaves.

Temporal and spatial detection of Candidatus Liberibacter asiaticus putative effector transcripts during interaction with Huanglongbing-susceptible, -tolerant, and -resistant citrus hosts.

Background: Citrus Huanglongbing (HLB) is a bacterial disease with high economic significance. The associated agent Candidatus Liberibacter asiaticus is a fastidious, phloem-limited, intracellular bacterium that is transmitted by an insect vector the Asian citrus psyllid (ACP). The genome of Ca.

Construction of High-Density Genetic Maps and Detection of QTLs Associated With Huanglongbing Tolerance in Citrus.

Huanglongbing (HLB), or citrus greening, is the most devastating disease in citrus worldwide. Commercial citrus varieties including sweet orange () are highly susceptible to HLB, and trifoliate orange (, a close relative) is widely considered resistant or highly tolerant to HLB. In this study, an intergeneric F population of sweet orange and trifoliate orange was genotyped by Genotyping-by-Sequencing, and high-density SNP-based genetic maps were constructed separately for trifoliate orange and sweet orange.

Epifluorescence and Stereomicroscopy of Trichomes Associated with Resistant and Susceptible Host Plant Genotypes of the Asian Citrus Psyllid (Hemiptera: Liviidae), Vector of Citrus Greening Disease Bacterium.

Background And Significance: Foliar trichomes (tiny hair-like structures) are part of the plant defense mechanisms that may confer resistance to some herbivore pests. Trifoliate orange, , is a genotype resistant to infestations by the Asian citrus psyllid, (Hemiptera: Liviidae), vector of the economically important citrus greening (huanglongbing) disease bacterium. We discovered that dense trichomes are associated with young leaves of trifoliate orange plants and hypothesized that these might be responsible for reduced infestation by this psyllid.

Identification of Gene Candidates Associated with Huanglongbing Tolerance, Using 'Candidatus Liberibacter asiaticus' Flagellin 22 as a Proxy to Challenge Citrus.

The 22-amino acid (flg22) pathogen-associated molecular pattern from the flagellin of Xanthomonas citri subsp. citri has been shown to induce defense responses correlated with citrus canker resistance. Here, flg22 of 'Candidatus Liberibacter asiaticus', the putative causal agent of Huanglongbing (HLB), elicited differential defense responses that were weaker than those from Xcc-flg22, between those of the HLB-tolerant mandarin cultivar Sun Chu Sha and susceptible grapefruit cultivar Duncan.

Transgenic expression of antimicrobial peptide D2A21 confers resistance to diseases incited by Pseudomonas syringae pv. tabaci and Xanthomonas citri, but not Candidatus Liberibacter asiaticus.

Citrus Huanglongbing (HLB) associated with 'Candidatus Liberibacter asiaticus' (Las) and citrus canker disease incited by Xanthomonas citri are the most devastating citrus diseases worldwide. To control citrus HLB and canker disease, we previously screened over forty antimicrobial peptides (AMPs) in vitro for their potential application in genetic engineering. D2A21 was one of the most active AMPs against X.

Comparative transcriptome analysis during early fruit development between three seedy citrus genotypes and their seedless mutants.

Identification of genes with differential transcript abundance (GDTA) in seedless mutants may enhance understanding of seedless citrus development. Transcriptome analysis was conducted at three time points during early fruit development (Phase 1) of three seedy citrus genotypes: Fallglo (Bower citrus hybrid (××)×Temple (×)), grapefruit (), Pineapple sweet orange (), and their seedless mutants. Seed abortion in seedless mutants was observed at 26 days post anthesis (Time point 2).

Accurate measurement of transgene copy number in crop plants using droplet digital PCR.

Genetic transformation is a powerful means for the improvement of crop plants, but requires labor- and resource-intensive methods. An efficient method for identifying single-copy transgene insertion events from a population of independent transgenic lines is desirable. Currently, transgene copy number is estimated by either Southern blot hybridization analyses or quantitative polymerase chain reaction (qPCR) experiments.

Novel R2R3-MYB transcription factors from Prunus americana regulate differential patterns of anthocyanin accumulation in tobacco and citrus.

The level of anthocyanins in plants vary widely among cultivars, developmental stages and environmental stimuli. Previous studies have reported that the expression of various MYBs regulate anthocyanin pigmentation during growth and development. Here we examine the activity of 3 novel R2R3-MYB transcription factor (TF) genes, PamMybA.

Long-Term Field Evaluation Reveals Huanglongbing Resistance in Citrus Relatives.

Citrus huanglongbing (HLB) is a destructive disease with no known cure. To identify sources of HLB resistance in the subfamily Aurantioideae to which citrus belongs, we conducted a six-year field trial under natural disease challenge conditions in an HLB endemic region. The study included 65 Citrus accessions and 33 accessions belonging to 20 other closely related genera.

Overexpression of a Modified Plant Thionin Enhances Disease Resistance to Citrus Canker and Huanglongbing (HLB).

Huanglongbing (HLB or citrus greening disease) caused by Candidatus Liberibacter asiaticus (Las) is a great threat to the US citrus industry. There are no proven strategies to eliminate HLB disease and no cultivar has been identified with strong HLB resistance. Citrus canker is also an economically important disease associated with a bacterial pathogen (Xanthomonas citri).

Transcriptome Profiling of Huanglongbing (HLB) Tolerant and Susceptible Citrus Plants Reveals the Role of Basal Resistance in HLB Tolerance.

Huanglongbing (HLB) is currently the most destructive disease of citrus worldwide. Although there is no immune cultivar, field tolerance to HLB within citrus and citrus relatives has been observed at the USDA Picos farm at Ft. Pierce, Florida, where plants have been exposed to a very high level of HLB pressure since 2006.

Reduced Susceptibility to Xanthomonas citri in Transgenic Citrus Expressing the FLS2 Receptor From Nicotiana benthamiana.

Overexpression of plant pattern-recognition receptors by genetic engineering provides a novel approach to enhance plant immunity and broad-spectrum disease resistance. Citrus canker disease associated with Xanthomonas citri is one of the most important diseases damaging citrus production worldwide. In this study, we cloned the FLS2 gene from Nicotiana benthamiana cDNA and inserted it into the binary vector pBinPlus/ARS to transform Hamlin sweet orange and Carrizo citrange.

The codA gene as a negative selection marker in Citrus.

The use of positive selectable marker genes is widespread in plant genetic transformation allowing transgenic cells to grow while repressing non-transgenic cells. Negative selectable markers, on the contrary, allow the repression or ablation of transgenic cells. The codA gene of Escherichia coli encodes cytosine deaminase that hydrolyzes 5-fluorocytosine (5-FC) into the cytotoxic compound 5 fluorouracil.

A family of small cyclic amphipathic peptides (SCAmpPs) genes in citrus.

Background: Citrus represents a crop of global importance both in economic impact and significance to nutrition. Citrus production worldwide is threatened by the disease Huanglongbing (HLB), caused by the phloem-limited pathogen Candidatus Liberibacter spp..

Induction of innate immune responses by flagellin from the intracellular bacterium, 'Candidatus Liberibacter solanacearum'.

Background: 'Candidatus Liberibacter solanacearum' (Lso) is a phloem-limited alphaproteobacterium associated with the devastating zebra chip disease of potato (Solanum tuberosum). Like other members of Liberibacter, Lso-ZC1 encodes a flagellin domain-containing protein (Fla Lso ) with a conserved 22 amino-acid peptide (flg22 Lso ). To understand the innate immune responses triggered by this unculturable intracellular bacterium, we studied the pathogen-associated molecular patterns (PAMPs) that triggered immunity in Nicotiana benthamiana, using the flg22 Lso peptide and the full length fla Lso gene.

Heat treatment eliminates 'Candidatus Liberibacter asiaticus' from infected citrus trees under controlled conditions.

Huanglongbing (HLB) is one of the most destructive diseases of citrus worldwide. The three known causal agents of HLB are species of α-proteobacteria: 'Candidatus Liberibacter asiaticus', 'Ca. L.

Characterizing the citrus cultivar Carrizo genome through 454 shotgun sequencing.

The citrus cultivar Carrizo is the single most important rootstock to the US citrus industry and has resistance or tolerance to a number of major citrus diseases, including citrus tristeza virus, foot rot, and Huanglongbing (HLB, citrus greening). A Carrizo genomic sequence database providing approximately 3.5×genome coverage (haploid genome size approximately 367 Mb) was populated through 454 GS FLX shotgun sequencing.