Syncytium gene expression in Glycine max[PI 88788] roots undergoing a resistant reaction to the parasitic nematode Heterodera glycines

The plant parasitic nematode, Heterodera glycines is the major pathogen of Glycine max (soybean). H. glycines accomplish parasitism by creating a nurse cell known as the syncytium from which it feeds. The syncytium undergoes two developmental phases. The first is a parasitism phase where feeding sites are selected, initiating the development of the syncytium. During this earlier phase (1–4 days post infection), syncytia undergoing resistant and susceptible reactions appear the same. The second phase is when the resistance response becomes evident (between 4 and 6 dpi) and is completed by 9 dpi. Analysis of the resistant reaction of G. max genotype PI 88788 (G. max[PI 88788]) to H. glycines population NL1-RHg/HG-type 7 (H. glycines[NL1-RHg/HG-type 7]) is accomplished by laser microdissection of syncytia at 3, 6 and 9 dpi. Comparative analyses are made to pericycle and their neighboring cells isolated from mock-inoculated roots. These analyses reveal induced levels of the jasmonic acid biosynthesis and 13-lipoxygenase pathways. Direct comparative analyses were also made of syncytia at 6 days post infection to those at 3 dpi (base line). The comparative analyses were done to identify localized gene expression that characterizes the resistance phase of the resistant reaction. The most highly induced pathways include components of jasmonic acid biosynthesis, 13-lipoxygenase pathway, S-adenosyl methionine pathway, phenylpropanoid biosynthesis, suberin biosynthesis, adenosylmethionine biosynthesis, ethylene biosynthesis from methionine, flavonoid biosynthesis and the methionine salvage pathway. In comparative analyses of 9 dpi to 6 dpi (base line), these pathways, along with coumarin biosynthesis, cellulose biosynthesis and homogalacturonan degradation are induced. The experiments presented here strongly implicate the jasmonic acid defense pathway as a factor involved in the localized resistant reaction of G. max[PI 88788] to H. glycines[NL1-RHg/HG-type 7].