Plant-parasitic nematodes are major agricultural pests worldwide and novel approaches to control them are sorely needed. We report the draft genome sequence of the root-knot nematode Meloidogyne incognita, a biotrophic parasite of many crops, including tomato, cotton and coffee. Most of the assembled sequence of this asexually reproducing nematode, totaling 86 Mb, exists in pairs of homologous but divergent segments. This suggests that ancient allelic regions in M. incognita are evolving toward effective haploidy, permitting new mechanisms of adaptation. The number and diversity of plant cell wall-degrading enzymes in M. incognita is unprecedented in any animal for which a genome sequence is available, and may derive from multiple horizontal gene transfers from bacterial sources. Our results provide insights into the adaptations required by metazoans to successfully parasitize immunocompetent plants, and open the way for discovering new antiparasitic strategies.Plant-parasitic nematodes are responsible for global agricultural losses amounting to an estimated $157 billion annually. Although chemical nematicides are the most reliable means of controlling root-knot nematodes, they are increasingly being withdrawn owing to their toxicity to humans and the environment. Novel and specific targets are thus needed to develop new strategies against these pests.The Southern root-knot nematode Meloidogyne incognita is able to infect the roots of almost all cultivated plants, making it perhaps the

Secreted parasitism proteins encoded by parasitism genes expressed in esophageal gland cells mediate infection and parasitism of plants by root-knot nematodes (RKN). Parasitism gene 16D10encodes a conserved RKN secretory peptide that stimulates root growth and functions as a ligand for a putative plant transcription factor. We used in vitro and in vivo RNA interference approaches to silence this parasitism gene in RKN and validate that the parasitism gene has an essential function in RKN parasitism of plants. Ingestion of 16D10 dsRNA in vitro silenced the target parasitism gene in RKN and resulted in reduced nematode infectivity. In vivo expression of 16D10 dsRNA in Arabidopsis resulted in resistance effective against the four major RKN species. Because no known natural resistance gene has this wide effective range of RKN resistance, bioengineering crops expressing dsRNA that silence target RKN parasitism genes to disrupt the parasitic process represents a viable and flexible means of developing novel durable RKN-resistant crops and could provide crops with unprecedented broad resistance to RKN.double-stranded RNA ͉ RNA interference ͉ broad resistance ͉ plant-parasitic nematode R oot-knot nematodes (RKN, Meloidogyne species) are the most economically important group of plant-parasitic nematodes worldwide, attacking nearly every food and fiber crop grown (1). Four common RKN species (M. incognita, M. javanica, M. arenaria, and M. hapla) account for 95% of all RKN infestations in agricultural land, with M. incognita being the most important species (2). These highly successful pathogens infect Ͼ1,700 host plant species and are devastating global agricultural pests (1). The most cost-effective and sustainable method for reducing RKN damage to food and fiber crops is to develop resistant plants that suppress nematode development and reproduction (3, 4). However, only a limited number of plant species are resistant to RKN, and there are many crops for which appropriate resistance loci have not been identified (4, 5). As with other plant resistance genes, the function of available RKN resistance genes involves recognition of specific RKN biotypes, rendering crops vulnerable to selection for virulent field populations (6, 7).Secreted proteins encoded by parasitism genes expressed in nematode esophageal gland cells are critical for the invading RKN to transform selected root vascular cells into elaborate feeding cells, called giant-cells (8-10). We recently reported that a peptide (16D10) secreted from the subventral esophageal gland cells of parasitic second-stage juveniles (J2) of RKN affects root growth by directly interacting with a specific domain of a putative plant SCARECROW-like transcription factor (11). The secreted 16D10 parasitism peptide is conserved across RKN species and appears to mediate an early signaling event in RKN-host interactions.RNAi, first characterized in Caenorhabditis elegans (12), has evolved into a powerful gene silencing tool for analysis of gene function in a wide variety of organisms (...

Soybean (Glycine max (L.) Merr.) is an important crop that provides a sustainable source of protein and oil worldwide. Soybean cyst nematode (Heterodera glycines Ichinohe) is a microscopic roundworm that feeds on the roots of soybean and is a major constraint to soybean production. This nematode causes more than US$1 billion in yield losses annually in the United States alone, making it the most economically important pathogen on soybean. Although planting of resistant cultivars forms the core management strategy for this pathogen, nothing is known about the nature of resistance. Moreover, the increase in virulent populations of this parasite on most known resistance sources necessitates the development of novel approaches for control. Here we report the map-based cloning of a gene at the Rhg4 (for resistance to Heterodera glycines 4) locus, a major quantitative trait locus contributing to resistance to this pathogen. Mutation analysis, gene silencing and transgenic complementation confirm that the gene confers resistance. The gene encodes a serine hydroxymethyltransferase, an enzyme that is ubiquitous in nature and structurally conserved across kingdoms. The enzyme is responsible for interconversion of serine and glycine and is essential for cellular one-carbon metabolism. Alleles of Rhg4 conferring resistance or susceptibility differ by two genetic polymorphisms that alter a key regulatory property of the enzyme. Our discovery reveals an unprecedented plant resistance mechanism against a pathogen. The mechanistic knowledge of the resistance gene can be readily exploited to improve nematode resistance of soybean, an increasingly important global crop.

ABSTRACT␤-1,4-Endoglucanases (EGases, EC 3.2.1.4) degrade polysaccharides possessing ␤-1,4-glucan backbones such as cellulose and xyloglucan and have been found among extremely variegated taxonomic groups. Although many animal species depend on cellulose as their main energy source, most omnivores and herbivores are unable to produce EGases endogenously. So far, all previously identified EGase genes involved in the digestive system of animals originate from symbiotic microorganisms. Here we report on the synthesis of EGases in the esophageal glands of the cyst nematodes Globodera rostochiensis and Heterodera glycines. From each of the nematode species, two cDNAs were characterized and hydrophobic cluster analysis revealed that the four catalytic domains belong to family 5 of the glycosyl hydrolases (EC 3.2.1, 3.2.2, and 3.2.3). These domains show 37-44% overall amino acid identity with EGases from the bacteria Erwinia chrysanthemi, Clostridium acetobutylicum, and Bacillus subtilis. One EGase with a bacterial type of cellulose-binding domain was identified for each nematode species. The leucine-rich hydrophobic core of the signal peptide and the presence of a polyadenylated 3 end precluded the EGases from being of bacterial origin. Cyst nematodes are obligatory plant parasites and the identified EGases presumably facilitate the intracellular migration through plant roots by partial cell wall degradation.