Molecular analysis of plant-parasitic nematodes during their interactions with wild-type and mutant Arabidopsis plants
Final Report Abstract
Root-knot nematodes are a serious problem in agriculture. Because of their broad host range, they can infect the roots of over 2,000 plant species, including a wide range of crop plants. Root-knot nematode infection can lead to stunted growth and reduced yield, and as a result, these soil-borne pests cause to billions of agricultural dollars in losses worldwide. To meet food security needs, there is pressure to develop novel, environmentally-friendly nematode resistance strategies, and this requires an understanding of the complex interaction between nematodes and host plants at a molecular level. Through this funded proposal, we have identified and characterized two novel nematode secreted proteins with key roles in nematode parasitism. We identified a protein called MiPFN3 that binds to actin monomers and affects the plant actin cytoskeleton. The actin cytoskeleton in the nematode feeding cell had been observed to be diffuse and fragmented. It was not clear if the nematode was secreting proteins with a direct role in this process or whether actin fragmentation was by-product of the transcriptional changes induced in the feeding cells. We have the first evidence that the actin depolymerization is a direct result of the nematode protein MiPFN3, which is secreted into the plant cell and which can sequester monomeric actin. Actin polymerization/depolymerization is just one of many processes that the nematode manipulates in the host plants. For example, the nematode must actively quell the plant immune system so that it can invade the root undetected. Through our research in nematode secreted proteins, we have discovered a nematode protein called Mh265 that helps the nematode suppress host defense responses, and in particular, it can suppress callose deposition. Callose is a defense response triggered during pathogen infection and is thought to hamper nematode root invasion and feeding site formation. We hypothesize that the root-knot nematode secretes Mh265 into the plant to decrease immuneinduced callose deposition and to facilitate infection. Future strategies could focus on “turningup” callose responses to help enhance nematode resistance plants. However, the plant relies on more than just callose to defend itself against pathogens. Some plant hormones are key in plant defense signaling, and we found that we could induce resistance against nematodes in the model plant Arabidopsis by exogenously applying methyl jasmonate or the jasmonic acid (JA)-mimic coronatine. Surprisingly, we also found that the JA-precursor called OPDA (12-oxo-phytodienoic acid) can act as a defense signaling molecule, and OPDA alone plays an important role in protecting plants against nematodes. This result is significant because all previous work in plant parasitic nematode-plant interactions had focused on JA as the primary defense signaling molecule. We will use the information about JA-induced resistance and OPDA-mediated signaling in future efforts to induce durable resistance to nematodes in crop plants.
Publications
- (2016). “OPDA has key role in regulating plant susceptibility to the root-knot nematode Meloidogyne hapla in Arabidopsis.” Frontiers in Plant Science, October 2016
Gleason, C., Leelarasamee, N., Meldau. D., and I. Feussner
(See online at https://doi.org/10.3389/fpls.2016.01565)
