Publications

4533

‘ 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.