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 (...
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.
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