Alteration of Nematode Gene Expression Results in Altered Infection Characteristics

The southern root-knot nematode, Meloidogyne incognita, is an important obligate plant parasite with evolutionary adaptations such as a hollow, protrusible stylet and esophageal gland secretory cells that enable successful invasion and parasitism of roots of multiple crop species. Previous studies have identified more than fifty candidate genes that encode effector proteins synthesized in root-knot nematode esophageal gland cells and secreted from the stylet into plant cells during parasitism. Many of these candidate parasitism genes are without significant homology to any gene currently listed in public databases. Functional analysis of three of these M. incognita putative parasitism genes, designated Mi35F03, Mi4D01 and Mi5G05 was conducted by overexpression in plant tissue and RNA interference (RNAi) gene silencing assays. The effects of constitutive expression of each parasitism gene product with (+SP) and without (-SP) the secretion signal peptide were analyzed in Arabidopsis thaliana plants. Overexpression of Mi35F03-SP and Mi4D01-SP led to a decrease in root length and increase in root branching in transgenic Arabidopsis thaliana. There were no changes in the shoot phenotype of Arabidopsis lines that expressed any of the three parasitism gene products with or without the signal peptide. Interestingly, overexpression of Mi35F03 +/- SP and Mi4D01 +/- SP lead to a significant (p = 0.05) decrease in the number of galls/gram of root. Expression of double-stranded RNA complementary in sequence to each M. incognita parasitism gene transcript in transformed A. thaliana was utilized as a reciprocal way to analyze for potential RNAi effects on root-knot nematode parasitism of the host roots. A significant reduction in the number of galls/gram, were observed in Arabidopsis lines expressing dsRNA of each gene. These findings indicate that Mi35F03, Mi4D01 and Mi5G05 play a role in root-knot nematode parasitism of host plants and support host-derived RNAi as a means to silence root-knot nematode parasitism genes and reduce nematode infection of plants.