Publications

4369

Abstract Citrus Huanglongbing and Citrus tristeza are two diseases that affect the citrus industry worldwide. The pathogens causing these diseases are the phloem-limited bacteria ‘Candidatus Liberibacter spp.’ (mainly Ca. L. asiaticus, CLas) and citrus tristeza virus (CTV). We recently found that both CLas and CTV could be acquired and retained by the Asian citrus psyllid Diaphorina citri. However, the mechanism through which CLas and CTV interact with the insect vectors and plant hosts has not been defined. In this study, an electrical penetration graph was used to study the feeding behavior of D. citri adults on four groups of Citrus reticulata Blanco cv. Hongjü plants: healthy, CLas-infected, CTV-infected, and CTV-CLas coinfected plants. Liquid chromatography with tandem mass spectrometry (LC–MS/MS) was applied to analyze the metabolites of the four groups of plants. The combined results are as follows: (1) The lowest number of metabolites were enriched in CTV-infected plants, which hardly influenced the feeding behavior of D. citri, suggesting that mild CTV strain (CT31) infection caused limited disorders in citrus plants compared with CLas infection; (2) Increased levels of L-arabinose and kaempferol in CTV-infected and CLas-CTV coinfected plants were suggested to contribute to increased penetration time during feeding of D. citri. CLas-infection increases the difficulty of finding appropriate feeding sites by the vector and results in xylem feeding for certain duration; (3) A significant reduction in α-linolenic acid metabolism in CLas-infected plants was found to be related to methyl jasmonate signaling, which induced resistance to D. citri and increased the duration of salivation. This effect was reversed by coinfection with CTV and was consistent with the phloem structure and carbohydrate accumulation alteration; (4) Stress response-associated 2'-hydroxygenistein and sakuranetin were highly upregulated flavonoid in CTV-CLas coinfected plants. This combinged with the anatomical alterations might interfere with D. citri feeding in the citrus phloem, as reflected by the time reduction of sap-sucking there. These findings will provide new insights into the interactions between CTV and CLas in citrus and the insect vector D. citri that transmiting these pathogens.

ABSTRACTRaccoons (Procyon lotor) are reservoirs for pathogens of other wildlife species, domestic animals, and humans, including several tick‐borne pathogens. A relatively understudied organism in raccoons is Candidatus Neoehrlichia procyonis which has been detected in raccoons from the southeastern United States. A related species in Europe and Asia, Neoehrlichia mikurensis, uses rodents as reservoirs and Ixodes spp. as vectors; however, studies on rodents suggest they are not susceptible to Ca. N. procyonis. N. mikurensis has been associated with cases of neoehrlichiosis in people and dogs, which emphasizes the need to better understand the natural history of Ca. N. procyonis. We conducted a molecular survey of raccoons from selected regions of the United States and Canada. Of 394 raccoons tested, 167 (42.4%) were confirmed to be positive for Ca. N. procyonis based on sequence analysis. There was spatial variation in prevalence with significantly higher prevalence (68%, 268/394) being detected in the Southeast region of the United States compared with all other regions, although a high prevalence (55.1%, 217/394) was detected in California. Lower prevalence was detected in the Midwest (3.8%, 15/394) and none of the raccoons from Canada were positive. These data suggest that Ca. N. procyonis is widespread in raccoon populations in the United States but there is spatial variation which may be related to vector distribution or some other factor. Although not known to infect hosts other than raccoons, neoehrlichiosis should be considered in cases of suspected ehrlichiosis in immunocompromised dogs or people that have no known etiologic agent.

ABSTRACT Citrus huanglongbing (HLB), caused by “ Candidatus Liberibacter” spp., is one of the most disastrous citrus diseases worldwide. HLB‐affected citrus fruits are significantly more acidic than healthy fruits. However, the molecular mechanism behind this phenomenon remains to be elucidated. Here, we report that HLB‐affected fruits have higher levels of citric acid (CA) than healthy fruits. Moreover, Citrus PH4 ( CitPH4 ), which encodes a MYB transcription factor that functions as a key regulator of CA accumulation, was upregulated in HLB‐affected fruits relative to healthy fruits. Heterologous overexpression of CitPH4 in tobacco ( Nicotiana tabacum ) plants enhanced tolerance to HLB. Subsequently, overexpression and gene‐editing experiments indicated that CitPH4 can affect the salicylic acid (SA) pathway, which directly binds to and activates the promoter of CsPBS3 , a key gene of SA biosynthesis. HLB‐affected fruits had higher SA levels than healthy fruits. Furthermore, application of SA activated CA biosynthesis and application of CA activated SA biosynthesis and signalling in citrus fruits and decreased “ Candidatus Liberibacter asiaticus” ( C Las) titres in infected leaves. This work suggests that CitPH4 is a key node between CA and SA, thus revealing crosstalk between defence responses and fruit quality in citrus.

AbstractCyanobacteria exhibit a vast diversity from polar to tropical environments. Though much work has been done on elucidating their biodiversity, knowledge on the occurrence, diversity and toxicity of benthic cyanobacteria is limited when compared to the planktonic forms. Integrating molecular techniques with ecological and morphological analyses has become essential in untangling cyanobacterial diversity, particularly for benthic taxa such as the cryptic “Lyngbya.” Molecular markers such as the 16S rRNA gene and whole genome sequencing have significantly improved the taxonomy of cyanobacteria. Building on these advancements, this study characterizes benthic cyanobacterial isolates from various locations in Florida, USA, and Orange Walk, Belize, resulting in the identification of a novel genus, Floridanema, and four new species (F. aerugineum, F. evergladense, F. flaviceps, and F. fluviatile). This new genus commonly occurs in canals, ponds, lakes and rivers. By integrating ecological, morphological, and genomic analyses, this study provides support for the family Aerosakkonemataceae and the establishment of the order Aerosakkonematales. The LC–MS data revealed that Floridanema strains do not produce microcystins, nodularin‐R, or anabaenopeptins.