Changes in the Expression of Genes in Soybean Roots Infected by Nematodes

Abstract

1.1 Plant nematodes Plant parasitic nematodes cause severe damage to plants and are responsible for billions of dollars of losses worldwide (Koenning et al. 2007). Soybean cyst nematode (SCN; Hederodera glycines; Fig. 1a ) and root-knot nematode (RKN; Meloidogyne spp.; Fig. 1b) are sedentary obligate parasites of plants. SCN is the major pest of soybean and causes an estimated one billion dollars in losses annually in the US (Wrather & Koenning 2006). RKN is a major pest of vegetables and can become a serious problem on soybean, especially on edible soybean planted in areas used to grow vegetables (Adegbite & Adesiyan 2005). The genera Meloidogyne is widespread and is considered, economically and agriculturally, as a very important group of plant pathogens. The host range of Meloidogyne is very wide as it attacks almost all plant species (Sasser 1980). Both SCN and RKN are sedentary endoparasites and they cause dramatic morphological and physiological changes in plant cells while inflicting severe decreases on yield. Chemical methods of nematode control are costly and can damage the environment, especially with contamination of ground water. Therefore, the preferred method of nematode control is the use of resistant or tolerant varieties, when available. Unfortunately, a plant with resistance to one population of nematode is often susceptible to a different population due to the wide genetic variation of nematode populations. When a plant parasitic nematode infects a plant root, the nematode and the plant enters an intricate interactive relationship with the host that is attempting to inhibit nematode development, while the nematode’s goal is to develop and reproduce. The life cycle of SCN and cellular responses of soybean to SCN infection have been documented and reviewed extensively (Bird & Koltai 2000; Endo 1964; Endo, 1965; Endo, 1992; Goverse et al. 2000; Lilley et al. 2005; Mitchum & Baum 2008; Niblack et al. 2006; Williamson & Gleason 2003; Abad & Williamson 2010; Klink et al. 2011a). The SCN egg can be found in soil and within the mature female. The second stage juvenile (J2) hatches from the egg, searches for a root of a plant host, penetrates the root epidermis, and migrates intracellularly, using its stylet and enzyme secretions to disrupt cells and force its way toward the vascular tissue.