Color morphology of Diaphorina citri influences interactions with its bacterial endosymbionts and ‘Candidatus Liberibacter asiaticus’

Abstract

Diaphorina citri is a vector of ‘ Candidatus Liberibacter asiaticus, ’ ( C Las), associated with Huanglongbing, (HLB, or citrus greening) disease in citrus. D . citri exhibits three different color morph variants, blue, gray and yellow. Blue morphs have a greater capacity for long-distance flight as compared to non-blue morphs, but little else is known about how color morphology influences vector characteristics. In this study, we show that the color morphology of the insect is derived from pigmented cells of the fat body. Blue morphs acquire a lower level of C Las in their bodies from infected trees as compared to their gray and yellow conspecifics, referred to in this paper collectively as non-blue morphs. Accordingly, C Las titer in citrus leaves inoculated by non-blue insects was 6-fold higher than in leaves inoculated by blue insects. Blue color morphs harbored lower titers of Wolbachia and ‘ Candidatus Profftella armatura,’ two of the D . citri bacterial endosymbionts. Expression of hemocyanin, a copper-binding oxygen transport protein responsible for the blue coloration of hemolymph of other arthropods and mollusks, was previously correlated with blue color morphology and is highly up-regulated in insects continuously reared on C Las infected citrus trees. Based on our results, we hypothesized that a reduction of hemocyanin expression would reduce the D . citri immune response and an increase in the titer of C Las would be observed. Surprisingly, a specific 3-fold reduction of hemocyanin-1 transcript levels using RNA silencing in blue adult D . citri morphs had an approximately 2-fold reduction on the titer of C Las. These results suggest that hemocyanin signaling from the fat body may have multiple functions in the regulation of bacterial titers in D . citri , and that hemocyanin is one of multiple psyllid genes involved in regulating C Las titer.

Friend or foe? Relationship between ‘Candidatus Liberibacter asiaticus’ and Diaphorina citri

“…Thus, the authors hypothesized that the reduction of hemocyanin expression would reduce the D. citri immune response and an increase in the titer of Las would be observed. However, Las titers decreased slightly in response to hemocyanin silencing (Hosseinzadeh et al 2019).…”

Development on Citrus medica infected with ‘Candidatus Liberibacter asiaticus’ has sex-specific and -nonspecific impacts on adult Diaphorina citri and its endosymbionts

“…This hemocyanin was also more abundant in mixed sex nymphs and adults when exposed to CLas [25]. Although this hemocyanin is impacted quite consistently by CLas exposure and directly interacts with CLas, when Hosseinzadeh et al knocked down its expression they unexpectedly found evidence of lower CLas density [108]. This highlights the importance of directly investigating potential anti-CLas D. citri responses to determine the impact on CLas transmission.…”

Lessons from One Fastidious Bacterium to Another: What Can We Learn about Liberibacter Species from Xylella fastidiosa

“…D. citri is a genetically heterogeneous, sexually reproducing species, and the genetic background of individual insects can influence their interactions with C. Las. A recent study showed that D. citri color morphology impacts its vectoring capacity [133]. D. citri can be found in three color morphs: blue, yellow, and gray.…”

“…Blue individuals were found to harbor a lower titer of C. Las and the other bacterial endosymbionts, and transmit the pathogen less efficiently. A copper binding protein called hemocyanin, which is thought to be responsible for the insects’ blue color, may be responsible for these effects [133]. Vector competency has also been shown to vary naturally among D. citri populations, and to be heritable over many generations [134].…”