Genetic variation for disease resistance and tolerance among Arabidopsis thaliana accessions

Abstract

Pathogens can be an important selective agent in plant evolution because they can severely reduce plant fitness and growth. However, the role of pathogen selection on plant evolution depends on the extent of genetic variation for resistance traits and their covariance with host fitness. Although it is usually assumed that resistance traits will covary with plant fitness, this assumption has not been tested rigorously in plant-pathogen interactions. Many plant species are tolerant to herbivores, decoupling the relationship between resistance and fitness. Tolerance to pathogens can reduce selection for resistance and alter the effect of pathogens on plant evolution. In this study, we measured three components of Arabidopsis thaliana resistance (pathogen growth, disease symptoms, and host fitness) to the bacteria Pseudomonas syringae and investigated their covariation to determine the relative importance of resistance and tolerance. We observed extensive quantitative variation in the severity of disease symptoms, the bacterial population size, and the effect of infection on host fitness among 19 accessions of A. thaliana infected with P. syringae. The severity of disease symptoms was strongly and positively correlated with bacterial population size. Although the average fitness of infected plants was smaller than noninfected plants, we found no correlation between the bacterial growth or symptoms expressed by different accessions of A. thaliana and their relative fitness after infection. These results indicate that the accessions studied vary in tolerance to P. syringae, reducing the strength of selection on resistance traits, and that symptoms and bacterial growth are not good predictors of host fitness.

The impact of parasitism on resource allocation in a fungal host: the case of Cryphonectria parasitica and its mycovirus, Cryphonectria Hypovirus 1

“…Adamo (1999) observed an increase in egg laying following the activation of the host immune system by injection of inert components of the cell wall of the bacteria Serratia marcescens , again suggesting an acceleration of reproduction in the face of probable parasitism. Similar changes in life history in response to parasitism also exist in plants, as do many cases of variation in life‐history traits involved in resistance or tolerance have been reported in Arabidopsis thaliana (Kover & Schaal, 2002; Pagán, Alonso‐Blanco, & Garcia‐arenal, 2008; Salvaudon & Shykoff, 2013) as well as in other plant species (Bruns, Carson & May, 2012). Surprisingly, in fungi, no clear evidence of parasite‐driven modifications on fungal life‐history traits has yet been reported, although conversely host genetic identity was found to alter resource allocation balance in two fungal pathogens, the oomycete Hyaloperonospora parasitica (Heraudet, Salvaudon, & Shykoff, 2008) and the basidiomycete Puccinia triticina (Pariaud et al., 2013).…”

High‐throughput quantitative luminescence assay of the growth in planta of Pseudomonas syringae chromosomally tagged with Photorhabdus luminescens luxCDABE

“…The potential impact of the bioluminescence assay for rapid, large-scale quantification of bacterial growth on populations of individual plants is well illustrated by the analysis of natural variation in basal resistance (Kover and Schaal, 2002). Thus the determination of bacterial growth in about 100 ecotypes by the standard method of scoring colony forming units in plate assays would have required a total of more than 3000 leaf discs in 300 sample tubes to be ground and then manipulated for analysis at three dilutions in triplicate, or for 900 plates to be manually scored.…”

Genetic Diversity and Disease Resistance in Leaf-Cutting Ant Societies

“…The key assumption for the genetic diversity/disease resistance hypothesis is therefore met in two polyandrous and one monoandrous social insect species. Giv- en that genetic variation for disease resistance is also common among other taxa (Ebert et al 1998;Little and Ebert 1999Carius et al 2001;Kover and Schaal 2002), it seems likely that it may be the case for many other social insects as well. Interestingly, the nature of the variation in resistance depended on the dose of parasite to which individuals were exposed.…”

“…The impact of a parasite upon such a group may be reduced if a group is made up of multiple genotypes, and if these genotypes vary in their resistance to a parasite. Genetic variation for resistance to parasites has been found in many nonsocial organ-isms (Ebert et al 1998;Carius et al 2001;Little and Ebert 1999Kover and Schaal 2002), and has recently been demonstrated in bumblebees and honeybees (Baer and Schmid-Hempel 2003;Palmer and Oldroyd 2003). Although the mechanism in these latter cases is not yet known, the cellular immune response in insects can vary between genotypes (Carlton et al 1992;Cotter and Wilson 2002).…”