Publications

4783

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 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.

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.