Publications

4634

‘ Candidatus Liberibacter asiaticus’ (Las) is a gram-negative bacterial pathogen associated with citrus huanglongbing (HLB) or greening disease. Las is transmitted by the Asian citrus psyllid (ACP) where it colonizes the phloem tissue, resulting in substantial economic losses to the citrus industry worldwide. Despite extensive efforts, effective management strategies against HLB remain elusive, necessitating a deeper understanding of the pathogen's biology. Las undergoes cell-to-cell movement through phloem flow and colonizes different tissues in which Las may have varying interactions with the host. Here, we investigate the transcriptomic landscape of Las in citrus seed coat vasculatures, enabling a complete gene expression profiling of Las genome and revealing unique transcriptomic patterns compared with previous studies using midrib tissues. Comparative transcriptomics between seed coat, midrib, and ACP identified specific responses and metabolic states of Las in different host tissue. Two Las virulence factors that exhibit higher expression in seed coat can suppress callose deposition. Therefore, they may contribute to unclogging sieve plate pores during Las colonization in seed coat vasculature. Furthermore, analysis of regulatory elements uncovers a potential role of LuxR-type transcription factors in regulating Liberibacter effector gene expression during plant colonization. Together, this work provides novel insights into the pathogenesis of the devastating citrus HLB. [Formula: see text] Copyright © 2025 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

The ongoing spread of X-disease, which is associated with ‘ Candidatus Phytoplasma pruni’, has resulted in severe economic losses for cherry and stone fruit growers in the U.S. Pacific Northwest in the last decade. Given that this pathogen is transmitted by polyphagous leafhopper species, primarily Colladonus montanus ssp. reductus and C. geminatus in the Pacific Northwest, alternative plant hosts present a significant management concern. Here, we surveyed phytoplasma incidence in non- Prunus plants found in and around stone fruit orchard borders and compared these results to the leafhopper feeding patterns through gut content analysis. We confirmed ‘ Ca. P. pruni’ infection in 21 plant species from 15 families. Of these, 15 species were commonly found in the diets of phytoplasma-carrying leafhoppers. Due to the abundance of common plant species, including Taraxacum, Malva, and Trifolium spp., alternative hosts were found across all growing seasons, although ‘ Ca. P. pruni’ titer was low (<102 cells) in most of these hosts. No geographic patterns were identified; instead, phytoplasma incidence and spread at individual orchards was related to the management of annual and biennial host species, thus removing preferred leafhopper feeding hosts. These data suggest that alternative host removal, along with the removal of infected trees, is an effective means of slowing disease spread.

The ‘Cuimi’ kumquat is a unique citrus cultivar known for its thin, crisp pulp and sweet, aromatic flavor. In addition to its use in fresh consumption and processing, this variety exhibits certain medicinal properties. This study aims to investigate the genetic diversity of the Huanglongbing (HLB) bacterium across different tissues of the ‘Cuimi’ kumquat, offering a theoretical basis for understanding the HLB epidemic in Dechang County, Sichuan. The research focuses on the absolute quantification of the HLB bacterium in seven specific tissues of the ‘Cuimi’ kumquat, including new leaves, upper phloem of branches, fruit peduncle, pith, fruit axis, old leaves, and lower phloem of branches. Additionally, the types and contents of prophages were identified in these tissues. In the same diseased branch group, Candidatus Liberibacter asiaticus (CLas) exhibited an uneven distribution, with the highest concentration detected in the pith, significantly surpassing levels found in the stem and leaf tissues (new leaves, upper phloem of branches, old leaves, lower phloem of branches). Infected fruit peduncles and pith slices showed noticeable shrinkage and collapse in the phloem. Prophage analysis indicated that multiple types of prophages could be simultaneously detected within the same infected ‘Cuimi’ kumquat branch. New shoot tissues contained both Type 2 and Type 4 prophages, with a relatively higher abundance of Type 4 and a lower abundance of Type 2. The relative abundance of Type 1 prophage in the fruit tissues was generally higher than in other tissues. CLas primarily accumulates in the fruit tissues of the ‘Cuimi’ kumquat, and the situation in Dechang County suggests that individual trees may be infected with multiple prophage strains simultaneously.