Publications

4513

‘ Candidatus Phytoplasma pruni’ is the causative agent of X-disease on peach ( Prunus persica) trees. Infected trees exhibit premature yellowing, leaf necrosis causing a shot-hole appearance, limb dieback, and eventual death. How pathogen infection leads to these symptoms is unknown. This study undertook a modern characterization of the disease by assessing the physiological and transcriptomic consequences of phytoplasma infection. Phytoplasma titer was high in the symptomatic tissues and undetected or low in asymptomatic tissues. Symptomatic leaves had a significant decrease in chlorophyll a, chlorophyll b, and carotenoids. Transcriptomic analysis showed alterations in genes related to phytohormone synthesis and signaling, circadian rhythms, lignification, and sugar synthesis and transport. Several transcripts that might be related to symptom development were identified. Collectively, these data give a much clearer picture of symptom development in ‘ Ca. P. pruni’-infected P. persica and provide several avenues for further research in determining how ‘ Ca. P. pruni’ interacts with its host to elicit the observed symptoms. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

‘ Candidatus Liberibacter solanacearum’ (Lso) is a phloem-limited pathogen associated with devastating diseases in members of the Solanaceae and Apiaceae and vectored by several psyllid species. Different Lso haplotypes have been identified, and LsoA and LsoB are responsible for diseases in Solanaceae crops. Our efforts are aimed at identifying pathogenicity factors used by this bacterium to thrive in different hosts. Bacterial secreted proteins can play a role in host colonization or the manipulation of the host immune responses; these proteins are called effectors. In this study, we identified six LsoB-specific proteins with a conserved secretion motif as well as a conserved N-terminal domain in the mature protein. These proteins had different expression and secretion patterns but a similar subcellular localization in Nicotiana benthamiana leaves, suggesting that they play different roles regardless of their conserved secretion motif. One of these proteins, CKC_04425, was expressed at high levels in the insect vector and the host plant, indicating that it could play a role in both the plant and insect hosts, whereas the others were mainly expressed in the plant. One protein, CKC_05701, was able to efficiently suppress programmed cell death and reactive oxygen species production, suggesting that it may have a virulence role in LsoB-specific pathogenesis.

Huanglongbing (HLB), caused by phloem-limited ‘ Candidatus Liberibacter asiaticus’ (CLas), is the primary limiting factor of production in most citrus regions of the world. After infection, CLas is transported systemically throughout the phloem tissues following the source-sink movement. Split-root rhizoboxes and one-sided graft inoculation above the split trunk was used to understand if the vertical distance of the inoculum source and different anatomical structures (grafted or seedling trees) can affect the speed of the CLas movement, as well as the effects of the seasonality on these movements. The time for CLas to reach the roots was not affected by either distance of the inoculum source or tree type. The seasonal infection period appears to have an important effect on CLas movement. Trees inoculated in the summer had fast and uniform movement (first detection at 4 weeks after inoculation). Plants inoculated in the winter had a slow and uneven movement (first CLas detection at 14 weeks after inoculation). Our results indicate that summer and spring are the seasons of CLas down and lateral movement, but this is independent of the vertical distance of the inoculum source or anatomical structures of the plants. The findings from this study aid in the management of HLB in the field, as well as improve the methods for CLas detection. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY 4.0 International license .