The Department of Nematology's weekly NEMA 250 seminar series is presented this week by:

Damaris Godinez-Vidal, Ph.D., Project Scientist, Groen Lab, Dept. Nematology, University of California, Riverside, CA

Seminar Title: “Gradients in belowground herbivory may drive geographic clines in root defenses"

Seminar Summary: The longstanding biotic interactions hypothesis predicts that plants at lower latitudes experience more significant herbivore pressure and should invest in stronger defenses. However, the evidence is mixed and heavily skewed towards aboveground defenses and herbivory. To address knowledge gaps on subterranean herbivory, we reanalyzed existing datasets of phenotypic variation in root defense against Meloidogyne spp. Root-knot nematodes (RKN) parasitize the roots of various plant hosts. Nematode herbivory is known to be temperature-driven, with higher RKN activity at lower latitudes. Strikingly, a latitudinal bias in plant defense against RKNs was visible in all plant populations of monocot and dicot species for which we were able to obtain data, and nematodes had lower fitness in plants from lower latitudes. Among the plant species in our data set was the genetic model Arabidopsis thaliana, which produces aliphatic glucosinolates (AGs) as defensive chemicals. Across European accessions of Arabidopsis, we identified a genetically based latitudinal cline in levels of specific AGs. Notably, long-chain AGs were higher at lower latitudes and negatively correlated with RKN fitness. Functional genetic experiments with Arabidopsis mutants in genes underlying long-chain AG accumulation were in keeping with an important role for these compounds in plant defense against RKN. Taken together, our observations and experiments find patterns consistent with higher herbivore pressure and stronger plant defense at lower latitudes.