Transgenic Strategies for Enhancement of Nematode Resistance in Plants

Abstract

Plant parasitic nematodes (PPNs) are obligate biotrophic parasites causing serious damage and reduction in crop yields. Several economically important genera parasitize various crop plants. The root-knot, root lesion, and cyst nematodes are the three most economically damaging genera of PPNs on crops within the family Heteroderidae. It is very important to devise various management strategies against PPNs in economically important crop plants. Genetic engineering has proven a promising tool for the development of biotic and abiotic stress tolerance in crop plants. Additionally, the genetic engineering leading to transgenic plants harboring nematode resistance genes has demonstrated its significance in the field of plant nematology. Here, we have discussed the use of genetic engineering for the development of nematode resistance in plants. This review article also provides a detailed account of transgenic strategies for the resistance against PPNs. The strategies include natural resistance genes, cloning of proteinase inhibitor coding genes, anti-nematodal proteins and use of RNA interference to suppress nematode effectors. Furthermore, the manipulation of expression levels of genes induced and suppressed by nematodes has also been suggested as an innovative approach for inducing nematode resistance in plants. The information in this article will provide an array of possibilities to engineer resistance against PPNs in different crop plants.

Keywords: R genes; RNAi; plant parasitic nematodes; plant resistance; protease inhibitors.

FIGURE 1

Above-ground and below-ground symptoms from different plant species in response to nematode infections. (A) Soybean plants infected with soybean cyst nematodes (Heterodera glycines) (http://www.extension.umn.edu, reproduced with the permission of Assoc. Prof. Malvick from UMN, US). (B) Infected and uninfected wheat plants with cereal cyst nematode H. avenae (Courtesy Prof. Honglian Li, China, reproduced with permission from Riley et al., 2009). (C–E) Roots of sponge gourd, carrots, and okra infected with root-knot nematode Meloidogyne incognita, respectively. (F) Arabidopsis roots showing development of cysts induced by beet cyst nematode H. schachtii.

FIGURE 2

The mechanism of RNA interference (RNAi), the double-stranded RNA (dsRNA) is processed by the plant dicer enzyme (A) into (B). Once the dsRNA is uptaken by the nematode from the plant cell while feeding (C), the processing from dsRNA to short interfering RNA (siRNA) can be executed by the nematode dicer. Then, the siRNA is recognized by the RNA-induced silencing (RISC) complex of the nematode (D) and its unwinding into sense and antisense strands takes place. A proportion of the RISC complex loaded with the antisense strand interacts with the corresponding mRNA in the nematode (E) as a result the mRNA is cleaved by the RISC (F) and subsequently degraded (G). Moreover, the targeted mRNA can be made double-stranded after binding of the siRNA, and this dsRNA is then processed to produce additional siRNAs, intensifying the initial silencing signal (Gheysen and Vanholme, 2007).