Publications

3810

Abstract Dactylopius species, known as cochineal insects, are the source of the carminic acid dye used worldwide. The presence of two Wolbachia strains in Dactylopius coccus from Mexico was revealed by PCR amplification of wsp and sequencing of 16S rRNA genes. A metagenome analysis recovered the genome sequences of Candidatus Wolbachia bourtzisii wDacA (supergroup A) and Candidatus Wolbachia pipientis wDacB (supergroup B). Genome read coverage, as well as 16S rRNA clone sequencing, revealed that wDacB was more abundant than wDacA. The strains shared similar predicted metabolic capabilities that are common to Wolbachia, including riboflavin, ubiquinone, and heme biosynthesis, but lacked other vitamin and cofactor biosynthesis as well as glycolysis, the oxidative pentose phosphate pathway, and sugar uptake systems. A complete tricarboxylic acid cycle and gluconeogenesis were predicted as well as limited amino acid biosynthesis. Uptake and catabolism of proline were evidenced in Dactylopius Wolbachia strains. Both strains possessed WO-like phage regions and type I and type IV secretion systems. Several efflux systems found suggested the existence of metal toxicity within their host. Besides already described putative virulence factors like ankyrin domain proteins, VlrC homologs, and patatin-like proteins, putative novel virulence factors related to those found in intracellular pathogens like Legionella and Mycobacterium are highlighted for the first time in Wolbachia. Candidate genes identified in other Wolbachia that are likely involved in cytoplasmic incompatibility were found in wDacB but not in wDacA.

Plants inoculated with the huanglongbing (HLB)-associated bacterium, Candidatus Liberibacter asiaticus (CLas) typically must be monitored for 8–10 months to identify differences in susceptibility between genotypes. Continuous light is reported to accelerate development of HLB symptoms and field observations suggest that trees girdled by tags or tree ties showed greater symptoms. Therefore, an experiment was conducted assessing HLB susceptibility as influenced by light/dark periods of 12 hours: 12 hours and 24 hours: 0 hours, in combination with scoring tree trunks to disrupt phloem. Sixty trees of each of three citrus genotypes (‘Kuharske’, previously shown to be HLB resistant; rough lemon, previously shown to be HLB tolerant; and ‘Valencia’, highly HLB susceptible) were bud grafted using two CLas-infected buds (rough lemon and citron) per tree on 26 Mar. 2012, and were placed in controlled growth rooms (one 12 hour light: 12 hour dark and one constant light) on 4 June 2012. Ten trees of each genotype in each growth room were scored 10 cm above the soil (cutting through the bark but not the wood) with a knife on 18 July 2012 and the scoring was repeated at the same scoring wounds on 30 Aug. 2012. Trees were removed from growth rooms on 12 Dec. 2012 and subsequently maintained in a greenhouse. At two to three month intervals between June 2012 and May 2013, HLB symptoms and stem diameter at 5 cm above the soil were assessed, and three leaves per tree were collected for quantitative polymerase chain reaction (qPCR) determination of CLas titer. Six months after inoculation and 3 months following imposition of treatments, the ‘Valencia’ scored in the 12 hour light: 12 hour dark regime, the ‘Valencia’ non scored trees in 24 hours of light and the ‘Kuharske’ scored trees in 24 hours of light displayed higher CLas titers than most other trees. After an additional two months, both scored and non-scored trees of all three genotypes in 24 hours of light had significantly elevated CLas titers compared with trees in 12 hour light: 12 hour dark regime, but within most treatments all three genotypes had titers which were not statistically different from each other. Growth of ‘Kuharske’ and rough lemon was enhanced; whereas ‘Valencia’ growth was reduced when graft-inoculated plants were maintained in continuous light. Scoring enhanced early CLas development in ‘Kuharske’ when combined with continuous light, had no effect in rough lemon, and showed inconsistent effects in ‘Valencia’. Although continuous lighting enhanced disease progression, it did not reveal differences in HLB susceptibility.