Endogenous soybean peptide overexpression: an alternative to protect plants against root-knot nematodes

Nematodes are pathogens of many important crops, including soybean. The main species found in Brazil are root-knot (Meloidogyne spp.), cyst (Heterodera glycines), root lesion (Pratylenchus brachyurus) and reniform (Rotylenculus reniformis) nematodes. Ureases are traditionally known for catalyzing the hydrolysis of urea to ammonia and carbon dioxide. Besides the main function, they present other independent biological roles, including toxic activities against insects, specially Coleoptera and Hemiptera, and fungi. In previous work, the DNA sequence encoding an insecticidal peptide - named Jaburetox - was identified in a Canavalia ensiformes urease gene. The recombinant Jaburetox exhibited toxicity against insects. Subsequently, the DNA sequence corresponding to Jaburetox was identified as part of the soybean Eu4 urease gene, with the resulting peptide named Soyuretox. In the present study, explants of soybean were transformed with Agrobacterium rhizogenes and ‘composite’ plants produced consisting of wild-type shoots and transgenic hairy roots overexpressing Soyuretox. Thereafter soybean plants overexpressing Soyuretox were obtained through bombardment transformation. Due to similarity between nematode and insect digestion mechanisms, we challenged composite and whole-transgenic plants with the nematode Meloidogyne javanica. Hairy roots overexpressing Soyuretox exhibited a significant reduction (48 %; p<0.05) in the average reproductive factor when compared with empty-vector transformed hairy roots. Transgenic plants overexpressing Soyuretox also exhibited significant reduction (37.5 %; p<0.05) in reproductive factor when compared with non-transformed plants. This study demonstrates the potential of Soyuretox in confering resistance against nematodes, representing a new alternative control method for nematodes in economically important crops.