Publications

4687

Abstract He.pat.in'co.la. Gr. neut. n. hêpar (gen. hêpatos) , liver; L. masc./fem. n. incola , inhabitant, dweller; N.L. masc. n. Hepatincola , a dweller of the liver. Pseudomonadota / Alphaproteobacteria / Rhodospirilalles / Candidatus Hepatincolaceae / Candidatus Hepatincola Candidatus Hepatincola is a genus of uncultured, obligately host‐associated bacteria originally discovered in the lumen of the midgut glands (hepatopancreas) of terrestrial isopods. In this niche, the bacteria exhibit a characteristic morphology: elongated rods with a stalk‐like appendage at one pole, which can be inserted between the microvilli of the midgut epithelium. All known members of the genus belong to two species ( Ca . Hepatincola porcellionum and a yet to be named Ca . Hepatincola sp.) associated with terrestrial isopods. However, closely related genera from the same family have been observed in numerous aquatic and terrestrial members of the Ecdysozoa (molting invertebrates). Ca . Hepatincola and closely related genera all have reduced genomes of about 1.3 Mb with low DNA G + C content ( c . 30%) and extremely limited biosynthetic capacities but rich in transporters to import essential nutrients and precursors from the environment. In line with its ecological niche (the host gut lumen, a nutrient‐rich environment) and genomic characteristics, Ca . Hepatincola is rather a nutrient scavenger than a nutrient provider for the host. Ca . Hepatincola was initially classified within the order Rickettsiales and later within the Holosporales , but recent phylogenomic analyses support its phylogenetic placement within the order Rhodospirillales . DNA G + C content (mol % ) : 30. Type species : Candidatus Hepatincola porcellionum Wang et al. (2004), CL1.

Abstract Krum.hol.zi.bac.te.ri.o'ta. N.L. neut. n. Krumholzibacterium , type genus of the type class of the phylum; L. neut. pl. n. suff. ‐ota , ending to denote a phylum; N.L. neut. pl. n. Krumholzibacteriota , the phylum of the class Krumholzibacteria. The phylum Candidatus Krumholzibacteriota was proposed to accommodate genomic assemblies of yet‐uncultured microorganisms. The type species, of the genus, Candidatus Krumholzibacterium zodletonense Zgenome0171 T was recovered from an anaerobic, sulfide‐ and sulfur‐rich spring in Southwestern Oklahoma, USA. The phylum comprises one described class, order, family, genus, and species. However, currently available genomes ( n  = 90) in GTDB (release 08‐RS214) are accommodated in 1 class, 6 orders, 8 families, 30 genera, and 58 species. Phylogenetically, the phylum is closely related to Gemmatimonadota and multiple phyla with no cultured representatives ( Ca . Edwardsbacteria, Ca . Eisenbacteria, Ca . Latescibacterota, Ca . Zixibacteria, 4572‐55, ARS69, GCA‐2686955, JAAXHH01, JABDJQ01, JAGLTZ01, JAGLYR01, TA06, TA06_A, and VGIX01); all of which are part of the FCB ( Fibrobacteres , Chlorobia , Bacteroidetes ) superphylum in the Gracilicutes clade. Candidatus Krumholzibacteriota genomes have mainly been recovered from marine, freshwater, engineered, and host‐associated ecosystems. The prevailing in‐situ conditions in sampled habitats, gene content analysis, and the use of predictive machine learning‐based approaches suggest a phylum‐wide preference for anaerobic conditions, mesophilic temperatures, circumneutral pH, and low salinities. Metabolically, the type species of the type genus of the phylum is predicted to be a fermentative anaerobe with preference for amino acids over sugars as substrates. Later studies indicate that some members of the phylum harbor respiratory capacities (dissimilatory sulfate reduction, dissimilatory sulfite reduction, iron‐reduction, and high‐affinity oxygen respiration with a few members possessing the potential for low‐affinity oxygen respiration), while others possess the machinery for anaerobic degradation of aromatic hydrocarbons. Finally, although all members of Candidatus Krumholzibacteriota remain uncultured, a representative of the phylum was enriched in a methane‐ and iron‐fed bioreactor inoculated with Bothnian Sea sediments. Type genus : Candidatus Krumholzibacterium Youssef et al. 2019, CL2.

Abstract A new distribution map is provided for Candidatus Phytoplasma rubi Malembic-Maher et al. Mollicutes: Acholeplasmatales: Acholeplasmataceae. Hosts: Rubus spp.

Abstract A new distribution map is provided for Candidatus Phytoplasma ziziphi Jung et al. Mollicutes: Acholeplasmatales: Acholeplasmataceae. Main host: jujube (Ziziphus jujuba), also other stone fruits.

ABSTRACT Ponkan mandarin ( Citrus reticulata cv. Ponkan) is an important fruit crop planted across different countries. One of its most devastating diseases is citrus huanglongbing (HLB), which is associated with infection by the bacterium Candidatus Liberibacter asiaticus ( C Las). Although studies on HLB in Ponkan mandarin have been conducted, symptom heterogeneity and its association with C Las titer under field conditions remain underexplored. We examined the association between symptom variation and C Las infection status in a Ponkan mandarin grove by categorizing symptoms at both the leaf and canopy (tree) level. Chlorotic leaves were sampled and classified into different categories, including leaves exhibiting interveinal chlorosis (Cat. A), those showing vein yellowing (Cat. B), and blotchy mottled leaves (Cat. C). Polymerase chain reaction (PCR) and quantitative PCR (qPCR) assays targeting C Las revealed that Cat. A leaves, which resembled nutrient-deficient leaves, had higher C Las detection rates and a larger proportion of samples with high C Las titers. Canopy-level assessment of symptom diversity within each tree also revealed that plants bearing Cat. A leaves were more likely to carry C Las and have high pathogen loads. The likelihood was also greater in trees with higher leaf symptom diversity. Additional prophage typing of the detected C Las strains revealed that leaf symptom variations were independent of prophage type difference. Nutrient analyses revealed reduced magnesium, manganese, and zinc contents in Cat. A leaves, indicating that leaves prone to C Las infection also exhibited nutrient deficiencies. These findings highlight the complexity of potential cultivar-specific associations between C Las and citrus under field conditions. IMPORTANCE Although it is well-established that HLB in Ponkan mandarin is associated with C Las infection, the relationship between leaf symptom variation in this cultivar and the presence and titer of C Las under complex field conditions remains unclear. By examining symptom heterogeneity in natural field conditions at both the leaf and canopy level, this study demonstrated that HLB leaf symptom variation in naturally infected Ponkan mandarin corresponds to differences in C Las presence and titer at both levels. Notably, although blotchy mottling is considered the typical leaf symptom of HLB, we found that C Las detection rates and titers tended to be greater in leaves showing nutrient deficiency-like symptoms, which contrasts with patterns in other citrus cultivars. Recognizing inconsistencies among cultivar-specific patterns is important for interpreting HLB symptoms, devising sampling strategies, and exploring uncharacterized factors affecting symptom expression under field conditions.

ABSTRACT The selective autophagy receptor NEIGHBOUR OF BRCA1 (NBR1) is a key regulator of plant immunity, but its role against bacterial pathogens remains poorly understood. Here, we demonstrated that overexpression of CsNBR1 confers citrus resistance to huanglongbing (HLB) caused by ‘ Candidatus Liberibacter asiaticus’ ( C Las). CsNBR1 can interact with multiple virulence effector proteins of C Las, including SDE5115, SDE1, SDE19 and SDE5, leading to their degradation via the autophagic pathway. In addition, expression of CsNBR1 in Nicotiana benthamiana mitigated the leaf curling and dwarfing phenotypes triggered by SDE1 by reducing the protein content of SDE1. These findings reveal that CsNBR1 positively regulates citrus defence against C Las by degrading its effector proteins via selective autophagy, providing both mechanistic insights and a potential target for resistance breeding.

Abstract Phytoplasmas are wall-less plant pathogens characterized by highly reduced genomes and limited metabolic capabilities, leading to an obligate host dependency. Since phytoplasma axenic cultivation has not yet been achieved, genomic approaches are essential to unravelling their biological and pathogenic traits. However, such insights are currently hindered by the scarcity of complete genomes and the lack of data for several clades, as is the case for the quarantine-relevant ‘ Candidatus Phytoplasma phoenicium’ (group 16SrIX-B), the causal agent of the severe stone-fruit disease almond witches’ broom (AlmWB). In this study, we present the complete genome sequence of the Lebanese strain F1A, which consists of a 552,248 bp chromosome with a 24.29% GC content and encodes 450 protein-coding genes. Comparative analyses with 16SrIX group draft genomes revealed high conservation among Lebanese AlmWB strains; however, comparisons with related 16SrIX-C phytoplasmas were limited by their low assembly completeness. Beyond providing a complete reference genome for this phytoplasma group, the F1A chromosome revealed distinct metabolic features. Strain F1A lacks the upper glycolytic pathway, indicating a metabolism that relies on glycerol-3-phosphate uptake and carboxylic acid fermentation. Notably, in addition to the conserved malate-to-acetate pathway, F1A encodes a complete citrate lyase complex, suggesting the potential for citrate utilization. Phylogenetic analysis of the associated 2-hydrocarboxylate symporter revealed the widespread occurrence of two phylogenetically distinct variants in phytoplasmas. Apart from the deduced metabolic capacities, the predicted effector repertoire shows similarities with those of other phytoplasmas, including proteins associated with branch proliferation and witches’ broom symptoms. Overall, these findings link genome reduction to host-dependent carboxylic acid metabolism in a quarantine-relevant phytoplasma, establishing a framework for comparative and functional studies of 16SrIX phytoplasmas and providing a basis for future investigations of AlmWB ecology and pathogenicity.