Interactions “Candidatus Liberibacter solanacearum”—Bactericera cockerelli: Haplotype Effect on Vector Fitness and Gene Expression Analyses

Abstract

“Candidatus Liberibacter solanacearum” (Lso) has emerged as a serious threat world-wide. Five Lso haplotypes have been identified so far. Haplotypes A and B are present in the Americas and/or New Zealand, where they are vectored to solanaceous plants by the potato psyllid, Bactericera cockerelli (Šulc) (Hemiptera: Triozidae). The fastidious nature of these pathogens has hindered the study of the interactions with their eukaryotic hosts (vector and plant). To understand the strategies used by these pathogens to infect their vector, the effects of each Lso haplotype (A or B) on psyllid fitness was investigated, and genome-wide transcriptomic and RT-qPCR analyses were performed to evaluate Lso gene expression in association with its vector. Results showed that psyllids infected with haplotype B had significantly lower percentage of nymphal survival compared to psyllids infected with haplotype A. Although overall gene expression across Lso genome was similar between the two Lso haplotypes, differences in the expression of key candidate genes were found. Among the 16 putative type IV effector genes tested, four of them were differentially expressed between Lso haplotypes, while no differences in gene expression were measured by qPCR or transcriptomic analysis for the rest of the genes. This study provides new information regarding the pathogenesis of Lso haplotypes in their insect vector.

Bactericera cockerelli vitellogenin‐6 like, a vitellogenin without a direct reproductive function?

“…These differences in gene expression between uninfected insects and insects exposed to LsoA-and LsoB-infected plants could be associated with the colonization of the insect AC or they could be in response to modifications of the plant's composition as a result of Lso infection (Wallis et al, 2015). The differences observed between insects exposed to LsoAand LsoB-infected plants may indicate differences in Lso pathogenicity between the haplotypes (Yao et al, 2016). However, neither the DUF1946 nor the von Willebrand factor type D domains were predicted in the protein; therefore, BcVg6-like protein might not be able to bind Lso.…”

“…To obtain colonies infected with LsoA and LsoB, respectively, insects from the Lso‐free colonies were transferred to tomato plants previously infected with LsoA or LsoB. Plants and insects were tested using SSR1 primers (Lin et al ., ) to define the Lso haplotype, as previously reported (Yao et al ., ).…”

“…To obtain colonies infected with LsoA and LsoB, respectively, insects from the Lso-free colonies were transferred to tomato plants previously infected with LsoA or LsoB. Plants and insects were tested using SSR1 primers (Lin et al, 2012) to define the Lso haplotype, as previously reported (Yao et al, 2016). Relative expression levels of BcVg6-like transcript showed a significant upregulation in ACs from LsoA-infected females, and in Lso-free females exposed to LsoB-infected plants compared to Lso-free (control) females.…”

Effects of “Candidatus Liberibacter solanacearum” (haplotype B) on Bactericera cockerelli fitness and vitellogenesis

“…The present study confirms previous findings (Yao et al ., ) that crosses between Lso B‐infected insects produce fewer eggs than crosses between Lso‐free psyllids. This result might support the observed trade‐off between immune defense and reproduction, both energetically demanding processes (Schwenke et al ., ).…”

“…Also, previously, it was shown that the effects of Lso infection in B. cockerelli can differ depending on the Lso haplotype. The infection with each Lso haplotype resulted in the decrease of B. cockerelli fecundity, but only the infection with Lso B reduced the nymphal survival (Yao et al ., ). On potato and silver leaf nightshade, Lso‐infected B. cockerelli nymphs developed faster than uninfected psyllids, but their mortality was higher (Thinakaran et al ., ).…”