Expression of soybean cyst nematode resistance in transgenic hairy roots of soybean

Transgenic hairy roots of soybean [Glycine max (L,) Merrill] induced by Agr obacterium rhizogenes support the complete life cycle of soybean cyst nemat ode (SCN, Heterodera glycines Ichinohe) in vitro. However, expression of SC N resistance in hairy soybean roots has not been investigated. A transgenic hairy root system would be useful in de,eloping an assay for candidate SCN resistance genes. The objectives of this study were to characterize transg ene expression in SCN-infected hairy soybean roots and to evaluate a transg enic hairy root system for investigations of resistance to SCN. Seedling co tyledons of the SCN-susceptible cultivars, Agassiz and Parker, and SCN-resi stant Bell and Faribault were infected with A. rhizogenes strain K599 trans formed with T-DNA binary vectors containing the, gusA gene fused to promote rs from either the cauliflower mosaic virus (CaMV 35S), Arabidopsis thalian a phenylalanine ammonia lyase (PAL), or bean (Phaseolus vulgaris L,) chalco ne synthase-8 (CNS) genes. Nine days after inoculating transgenic hairy roo ts with sterile J2 nematodes, CHS-regulated P-glucuronidase (GUS) staining at infection sites increased in hairy roots of resistant Faribault and decr eased in susceptible Agassiz. PAL-regulated GUS staining was absent at infe ction sites in hairy roots of resistant cultivars, but was increased in inf ection sites in susceptible cultivars, Thirty-fire days after inoculation w ith SCN, the mean number of cysts formed on hairy roots of the resistant cu ltivars was about 14% of the mean number of cysts formed on hairy roots of the susceptible cultivars, indicating that the SCN resistance phenotypes we re preserved in transgenic hairy roots. These results indicated that the tr ansgenic hairy soybean root system will be useful for investigating differe ntial transgene expression during nematode infection and evaluation of cand idate SCN resistance genes.