Genetics

Here, we report the draft genome sequence of “ Candidatus Izimaplasma sp.” strain ZiA1 (1.88 Mb and 29.6% G+C content).

AbstractA disease known as broccoli stunt, associated with “Candidatus Phytoplasma pruni”‐related strain, has been responsible by significant economic losses in crops grown in the State of São Paulo, Brazil. Previous investigations evidenced some species of leafhoppers observed in broccoli fields as potential vectors of the phytoplasma. In this study, the six species more frequently found in broccoli crops were collected to confirm that evidence. Group of five insects of each species were confined per broccoli seedling for an inoculation access period (IAP) of 48 hr. After the IAP, each group was tested for detection of phytoplasma. Evaluation of plants was performed 60 days after inoculation based on the presence of phytoplasma in their tissues. When transmission was positive, genomic fragments corresponding to 16S rDNA were sequenced both for the infected plants and its respective group of insects. The results revealed that the species Agallia albidula, Agalliana sticticollis, Atanus nitidus and Balcluta hebe were able to transmit phytoplasma to broccoli seedlings. Based on the estimates of transmission probability by single insects (P), the highest transmission rate was observed for A. nitidus (24.2%) and the lowest for B. hebe (1.9%). The sequencing of 16S rDNA revealed complete similarity between the sequences of the phytoplasma transmitted to broccoli test plants and the sequences of the phytoplasma found in the field‐collected leafhoppers. These findings support the inclusion of those species as vectors of phytoplasmas belonging to 16SrIII group in broccolis, providing additional information to improve management of this important disease of endemic occurrence.

AbstractOf late, the presence of Candidatus Phytoplasma trifolii was reported as a serious threat to the pepper crop in Zacatecas, México; therefore, asymptomatic and symptomatic pepper plants were collected from a commercial field among three samplings after the fruit set stage was reached. Total DNA was extracted using the CTAB‐based method and tested for phytoplasma using a nested PCR assay, followed by a BLAST, and restriction fragment length polymorphism (RFLP) analysis of 16S rDNA sequences, which confirmed the presence of phytoplasma group 16SrVI, “Candidatus Phytoplasma trifolii” in the symptomatic plants. As the metabolic pathways of pathogen‐infected plants tend to change, resulting in a biochemical differentiation with the noninfected plants, the polyphenolic compound concentrations were quantified from the vegetative tissues (root, stem, leaves and developed fruit/big bud) and were analysed based on a principal component analysis (PCA). Results revealed that, in general, plants tend to a progressive increase in total phenols, flavonoids, condensed tannins and anthocyanins related to the plants exposure to “Ca. P. trifolii” infection, and PCA demonstrated that almost 90% of the observed variance was explained by the first two components. Hence, the phenolic content of the plants increases as a response of the defence mechanism, which reflects its condition and resistance.

Huanglongbing ( HLB ), caused by ‘ Candidatus Liberibacter asiaticus’ (Las), is a devastating disease of citrus trees in Florida. Previous work showed that the rootstock cultivar Cleopatra mandarin ( Citrus reticulata ) has a higher population of Las in roots than Swingle citrumelo ( C. paradisi  ×  Poncirus trifoliata ). Las reduced fibrous root biomass and sucrose content in Cleopatra mandarin more than in Swingle citrumelo. To understand the mechanisms for susceptibility to Las infection, sucrose and hormone metabolism status were evaluated in Cleopatra mandarin and Swingle citrumelo. In fibrous roots of Cleopatra mandarin, higher expression of genes related to sucrose cleavage was consistent with lower sucrose content compared to noninoculated seedlings at 5 weeks post‐root trimming (wpt). In fibrous roots of Swingle citrumelo, both sucrose content and gene expression related to sucrose cleavage were less disrupted by Las infection compared to Cleopatra mandarin at 5 wpt. Genes associated with salicylic acid ( SA ), ethylene ( ET ) and abscisic acid ( ABA ) synthesis, and ABA signalling, phospholipases D ( PLD ), and phospholipase A2 ( PLA 2) were activated by Las infection at 5 wpt in Cleopatra mandarin. Expression of downstream effectors of SA , i.e. NPR 1, WRKY 70 and PR 1, did not change in Cleopatra mandarin, suggesting inhibition of the response to SA by the elevation of ABA , ET and PLD . In contrast, the up‐regulation of PR 1, lower response of sucrose metabolism genes and down‐regulation of biosynthesis of phytohormones indicates that Swingle citrumelo activates a more effective defence against this biotrophic pathogen than Cleopatra mandarin.

In this study, we present the genome sequence of the “ Candidatus Cardinium hertigii” strain cHgTN10, an endosymbiotic bacterium of the plant-parasitic nematode Heterodera glycines . This is the first genome assembly reported for an endosymbiont directly sequenced from a tylenchid nematode.

The draft genome sequence of “ Candidatus Liberibacter asiaticus” strain TX1712, obtained from a Texas citrus tree, is reported here. Strain TX1712 has a draft genome size of 1,203,333 bp, a G+C content of 36.4%, 1,230 predicted open reading frames, and 41 RNAs and comprises 97.4% of the psy62 reference genome.

ABSTRACT Here, we report the draft genome sequence of “ Candidatus Liberibacter europaeus” ASNZ1, assembled from broom psyllids ( Arytainilla spartiophila ) from New Zealand. The assembly comprises 15 contigs, with a total length of 1.33 Mb and a G+C content of 33.5%.