Shared transcriptional control and disparate gain and loss of aphid parasitism genes

Aphids are a diverse group of taxa that contain agronomically important species, which vary in their host range and ability to infest crop plants. The genome evolution underlying agriculturally important aphid traits is not well understood. We generated draft genome assemblies for two aphid species: Myzus cerasi (black cherry aphid), and the cereal specialist Rhopalosiphum padi. Using a de novo gene prediction pipeline on both these, and three additional aphid genome assemblies (Acyrthosiphon pisum, D. noxia and M. persicae), we show that aphid genomes consistently encode similar gene numbers. We compare gene content, gene duplication, synteny, and putative effector repertoires between these five species to understand the genome evolution of globally important plant parasites. Aphid genomes show signs of relatively distant gene duplication, and substantial, relatively recent, gene birth. Putative effector repertoires, originating from duplicated and other loci have an unusual genomic organisation and evolutionary history. We identify a highly conserved effector-pair that is tightly physically-linked in the genomes of all aphid species tested. In R. padi, this effector pair is tightly transcriptionally-linked, and shares an unknown transcriptional control mechanism with a subset of approximately 50 other putative effectors and secretory proteins. This study extends our current knowledge on the evolution of aphid genomes and reveals evidence for an as of yet unknown shared control mechanism, which underlies effector expression, and ultimately plant parasitism

Signatures of adaptation to a monocot host in the plant-parasitic cyst nematode Heterodera sacchari.

Interactions between plant-parasitic nematodes and their hosts are mediated by effectors, i.e. secreted proteins that manipulate the plant to the benefit of the pathogen. To understand the role of effectors in host adaptation in nematodes, we analysed the transcriptome of Heterodera sacchari, a cyst nematode parasite of rice (Oryza sativa) and sugarcane (Saccharum officinarum). A multi-gene phylogenetic analysis showed that H. sacchari and the cereal cyst nematode Heterodera avenae share a common evolutionary origin and that they evolved to parasitise monocot plants from a common dicot-parasitic ancestor. We compared the effector repertoires of H. sacchari with those of the dicot parasites Heterodera glycines and Globodera rostochiensis to understand the consequences of this transition. While, in general, effector repertoires are similar between the species, comparing effectors and non-effectors of H. sacchari and G. rostochiensis shows that effectors have accumulated more mutations than non-effectors. Although most effectors show conserved spatiotemporal expression profiles and likely function, some H. sacchari effectors are adapted to monocots. This is exemplified by the plant-peptide hormone mimics, the CLAVATA3/EMBRYO SURROUNDING REGION-like (CLE) effectors. Peptide hormones encoded by H. sacchari CLE effectors are more similar to those from rice than those from other plants, or those from other plant-parasitic nematodes. We experimentally validated the functional significance of these observations by demonstrating that CLE peptides encoded by H. sacchari induce a short root phenotype in rice, whereas those from a related dicot parasite do not. These data provide a functional example of effector evolution that co-occurred with the transition from a dicot-parasitic to a monocot-parasitic lifestyle.BBSR

How parasitism genes are regulated: a motif to search for genes regulators in the plant parasitic nematode Bursaphelenchus xylophilus

Plant-parasitic nematodes threaten global agricultural and forestry systems. The search for new control strategies in line with the EU’s sustainability goals highlight significant knowledge gaps. Like all other plant pathogens, plant-parasitic nematodes deliver several parasitism proteins (effectors) into the host plant to cause disease. NemaWAARS project focuses on mechanism(s) of regulation and gene control expression of parasitism genes in pinewood nematode, Bursaphelenchus xylophilus. From the previous transcriptomic data derived from the pharyngeal gland cells (considered a specialized tissue potentially related to parasitism) we have identified a non-coding DNA motif - STATAWAARS - associated in the promotor region of highly abundant and secreted expressed genes. Given that this non-coding genetic signature unifies many sequences of unrelated parasitism genes, it implies the existence of a potential major regulator(s), that binds to this sequence to control the expression of downstream genes. We hypothesize that by disrupting this regulator(s), it would be possible to simultaneously disrupt the expression of many associated parasitism-related genes. To test the hypothesis the project aims to identify proteins (or complex of proteins) that bind in the promoter regions of parasitism-related genes (in vivo) or identify other regulatory candidates for master regulators of parasitism-related genes expression that are enriched in the pharyngeal gland cell tissues. For the best candidate regulatory proteins, an RNAi approach will target the selected gene candidates and evaluate the regulatory role in effector genes expression and in interaction with the host (in planta). Under an ongoing national and international collaborative network, the strategy in NemaWAARS will include innovative approaches to explore the regulators that govern effector gene expression applied in B. xylophilus research

A genomic resource for the sedentary semi-endoparasitic reniform nematode, Rotylenchulus reniformis Linford & Oliveira.

The reniform nematode (Rotylenchulus reniformis) is a sedentary semi-endoparasitic species that is pathogenic on many row crops, fruits, and vegetables. Here, the authors present a draft genome assembly of R. reniformis using small- and large-insert libraries sequenced on the Illumina GAIIx and MiSeq platforms. The reniform nematode (Rotylenchulus reniformis) is a sedentary semi-endoparasitic species that is pathogenic on many row crops, fruits, and vegetables. Here, the authors present a draft genome assembly of R. reniformis using small- and large-insert libraries sequenced on the Illumina GAIIx and MiSeq platforms

The <i>Pratylenchus penetrans</i> transcriptome as a source for the development of alternative control strategies:mining for putative genes involved in parasitism and evaluation of <i>in planta</i> RNAi

The root lesion nematode Pratylenchus penetrans is considered one of the most economically important species within the genus. Host range studies have shown that nearly 400 plant species can be parasitized by this species. To obtain insight into the transcriptome of this migratory plant-parasitic nematode, we used Illumina mRNA sequencing analysis of a mixed population, as well as nematode reads detected in infected soybean roots 3 and 7 days after nematode infection. Over 140 million paired end reads were obtained for this species, and de novo assembly resulted in a total of 23,715 transcripts. Homology searches showed significant hit matches to 58% of the total number of transcripts using different protein and EST databases. In general, the transcriptome of P. penetrans follows common features reported for other root lesion nematode species. We also explored the efficacy of RNAi, delivered from the host, as a strategy to control P. penetrans, by targeted knock-down of selected nematode genes. Different comparisons were performed to identify putative nematode genes with a role in parasitism, resulting in the identification of transcripts with similarities to other nematode parasitism genes. Focusing on the predicted nematode secreted proteins found in this transcriptome, we observed specific members to be up-regulated at the early time points of infection. In the present study, we observed an enrichment of predicted secreted proteins along the early time points of parasitism by this species, with a significant number being pioneer candidate genes. A representative set of genes examined using RT-PCR confirms their expression during the host infection. The expression patterns of the different candidate genes raise the possibility that they might be involved in critical steps of P. penetrans parasitism. This analysis sheds light on the transcriptional changes that accompany plant infection by P. penetrans, and will aid in identifying potential gene targets for selection and use to design effective control strategies against root lesion nematodes