Physiology

The Asian citrus psyllid Diaphorina citri is the transmission vector of Huanglongbing (HLB), a devastating disease of citrus plants. The bacterium “Candidatus Liberibacter asiaticus” (CLas) associated with HLB is transmitted between host plants by D. citri in a circulative manner. Understanding the interaction between CLas and its insect vector is key for protecting citrus cultivation from HLB damage. Here, we used RNA sequencing and liquid chromatography-mass spectrometry (LC-MS) to analyze the transcriptome and metabolome of D. citri interacting with CLas. We identified 662 upregulated and 532 downregulated genes in CLas-infected insects. These genes were enriched in pathways involving carbohydrate metabolism, the insects’ immune system, and metabolism of cofactors and vitamins. We also detected 105 differential metabolites between CLas-infected and non-infected insects, including multiple nucleosides and lipid-related molecules. The integrated analysis revealed nine pathways—including those of the glycine, serine, threonine, and purine metabolism—affected by the differentially expressed genes from both groups. The network for these pathways was subsequently constructed. Our results thus provide insights regarding the cross-talk between the transcriptomic and metabolomic changes in D. citri in response to CLas infection, as well as information on the pathways and genes/metabolites related to the CLas–D. citri interaction.

Ammonia tolerance of AOA is usually much lower than that of the AOB, which makes the AOB rather than AOA a predominant ammonia oxidizer in agricultural soils, contributing to global N 2 O emission. Recently, some AOA species from the genus “ Ca. Nitrosocosmicus” were also found to have high ammonia tolerance.

Microbiology is in a new age in which sequence databases are primary sources of information about many microbes. However, in-depth analysis of environmental genomes thus retrieved is essential to substantiate the new knowledge.

Sec-delivered effector 1 (SDE1) from the huanglongbing (HLB)-associated bacterium ‘Candidatus Liberibacter asiaticus’ was previously characterized as an inhibitor of defense-related, papain-like cysteine proteases in vitro and in planta. Here, we investigated the contributions of SDE1 to HLB progression. We found that SDE1 expression in the model plant Arabidopsis thaliana caused severe yellowing in mature leaves, reminiscent of both ‘Ca. L. asiaticus’ infection symptoms and accelerated leaf senescence. Induction of senescence signatures was also observed in the SDE1-expressing A. thaliana lines. These signatures were apparent in older leaves but not in seedlings, suggesting an age-associated effect. Furthermore, independent lines of transgenic Citrus paradisi (L.) Macfadyen (Duncan grapefruit) that express SDE1 exhibited hypersusceptibility to ‘Ca. L. asiaticus’. Similar to A. thaliana, transgenic citrus expressing SDE1 showed altered expression of senescence-associated genes, but only after infection with ‘Ca. L. asiaticus’. These findings suggest that SDE1 is a virulence factor that contributes to HLB progression, likely by inducing premature or accelerated senescence in citrus. This work provides new insight into HLB pathogenesis. [Formula: see text] Copyright © 2020 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

AbstractCandidatus Liberibacter solanacearum haplotype B (CLsoB) is an economically important pathogen of tomato (Solanum lycopersicum L.) crops in New Zealand and Central and North America. Currently, resistant cultivars of tomato are not available as a management tactic because breeding programmes lack sources of resistance. Therefore, the objective of this study was to identify sources of resistance in tomato to CLsoB. Forty‐six landraces of tomato were collected from several states in Mexico and were inoculated with CLsoB using 20 infested adults of Bactericera cockerelli per plant. Two assays were done over two years under greenhouse conditions. In the first trial, landraces FC22 and FC44 showed a significantly higher proportion of resistant plants, less symptom severity and longer incubation time compared with the other forty‐four landraces and two susceptible cultivars. In the second assay, resistance to CLsoB of the landraces FC22 and FC44 was confirmed because they had again significantly greater numbers of resistant plants, less symptom severity, relative lower CLsoB titers and longer incubation time relative to the other genotypes. All plants considered resistant from both assays had DNA of CLsoB. Results indicate that all resistant plants from these landraces are promising sources for the development of tomato cultivars with resistance to CLsoB.