Many plant-parasitic nematodes hatch out of their eggs as a developmentally arrested pre-infective juveniles (L2) that share functional similarity to C. elegans dauers. Nothing is known about the genetic programming of development in these nematodes or how it may be linked to environmental cues. Nevertheless, it is likely that plant-parasitic nematodes use molecules similar to those defined by the C. elegans dauer pathway to regulate developmental arrest, lifespan, and chemosensation. The long-range goal of this research is to determine the molecular mechanisms controlling plant-parasitic nematode development in order to discover new targets for safe, specific and biologically based methods for controlling these damaging pathogens. The
daf-21 gene from C. elegans encodes a molecular chaperone of the Hsp90 class (Birnby, et al., 2000). Mutation of
daf-21 is dauer-constitutive, and has been shown to cause defects in chemosensory responses mediated by several classes of chemosensory neurons. The precise function of
daf-21 in the dauer pathway is unclear. However, Hsp90 chaperones are known to refold denatured or misfolded proteins, especially under conditions of stress. In C. elegans , transcription of Hsp90 is increased 15-fold in dauers versus non-dauers, which would be consistent with this type of protective function (Dalley and Golomb, 1992). Under non-stress conditions, Hsp90 has been shown to guide the proper folding of specific target proteins, including nuclear hormone receptors and protein kinases. Possible targets of Hsp90 in C. elegans include the
daf-11 transmembrane guanylate cyclase, the
daf-5 putative Sno transcription factor, and the
daf-12 nuclear hormone receptor. Additionally, the C. elegans aryl hydrocarbon receptor, AHR-1, has been shown to bind to Hsp90 (Powell-Coffman, et al ., 1998), suggesting
daf-21 involvement in the response to environmental pollutants. We have focused on the cloning and characterization of Hsp90 (
daf-21 ) from several species of plant-parasitic nematodes of economic concern to agriculture. We have obtained full-length cDNA and partial genomic sequence from the soybean cyst nematode, Heterodera glycines , and are in the process of examining expression of the gene and its protein product. In addition, we have developed a set of PCR primers that amplify a portion of the Hsp90 gene from single nematode extracts. This technique has enabled us to isolate partial Hsp90 sequence from a wide range of agriculturally important nematodes, including cyst, root-knot, and lesion nematodes. We have identified variation in intron number and position in this amplification segment within the root-knot nematodes. This variation may comprise a useful diagnostic for several nematodes of agricultural concern, so we are now expanding this study to include more taxa. Hsp90 is a highly conserved protein whose sequence has been extensively used in determining the evolutionary relationships between eubacteria, archaebacteria, and eukaryotes (Gupta, 1998). Mutations in Hsp90 have been shown to unmask hidden genetic variation in fruit flies (Rutherford and Lindquist,1998) and therefore may play a critical role in regulating the evolutionary potential of an organism. Whether this phenomenon holds true for nematodes is unclear, however, we hope to gain insight into the function of plant-parasitic nematode Hsp90’s by examining the sequences from a phylogenetic perspective. Birnby, et al., 2000. Genetics 155:85-104. Dalley and Golomb, 1992. Developmental Biology 151: 80-90. Powell-Coffman, et al., 1998. PNAS,95:2844-2849. Gupta, 1998. Microbiology and Molecular Biology Reviews. 62:1435-1491. Rutherford and Lindquist, 1998. Nature 396: 336-342.