Eighteen new candidate effectors of the phytonematode heterodera glycines produced specifically in the secretory esophageal gland cells during parasitism

Abstract

Heterodera glycines, the soybean cyst nematode, is the number one pathogen of soybean (Glycine max). This nematode infects soybean roots and forms an elaborate feeding site in the vascular cylinder. H. glycines produces an arsenal of effector proteins in the secretory esophageal gland cells. More than 60 H. glycines candidate effectors were identified in previous gland-cell-mining projects. However, it is likely that additional candidate effectors remained unidentified. With the goal of identifying remaining H. glycines candidate effectors, we constructed and sequenced a large gland cell cDNA library resulting in 11,814 expressed sequence tags. After bioinformatic filtering for candidate effectors using a number of criteria, in situ hybridizations were performed in H. glycines wholemount specimens to identify candidate effectors whose mRNA exclusively accumulated in the esophageal gland cells, which is a hallmark of many nematode effectors. This approach resulted in the identification of 18 new H. glycines esophageal gland-cell-specific candidate effectors. Of these candidate effectors, 11 sequences were pioneers without similarities to known proteins while 7 sequences had similarities to functionally annotated proteins in databases. These putative homologies provided the bases for the development of hypotheses about potential functions in the parasitism process.