Some biotrophic plant pathogens have the remarkable ability to alter plant developmental morphology and subcellular architecture.At least three examples of this ability arose independently within the phylum Nematoda.For one such example,the cyst nematodes,plant cell manipulation is rapid and profound;within days the cell cycle of a single cell in the vascular cylinder is arrested at G2,the vacuole reduces in size and fragments,the nucleus greatly enlarges,the cytoplasm is enriched in subcellular organelles by extensive proliferation of the smooth endoplasmic reticulum,ribosomes,mitochondria,and plastids (chloroplasts and amyloplasts),and the cell wall is degraded to promote protoplast fusion in an iterative manner,ultimately incorporating hundreds of adjacent cells (Figure 1;Jones,1981).