In prior studies, our lab found that costs of resistance to pathogens in the absence of disease was ~5-10% for the resistance (R) genes Rps5 and Rpm1, respectively. However, Arabidopsis thaliana has 149 R-genes so it is unlikely that many R genes incur such a high cost. The now published research of former PhD student Alice MacQueen focuses on Rps2 that exists as an ancient balanced polymorphism with two long-lived clades of alleles. Alice conducted field trials that show that Arabidopsis thaliana plants with resistant Rps2 are no less fit than those with a susceptible Rps2 allele in the absence of disease. Both resistant and susceptible Rps2 alleles contribute to controlling defense and stress gene expression thus presenting a pleiotropic effect to explain the maintenance of both alleles.
We are excited that Ana-Lisa Laine reviews the significance of Alice’s work in
Disease resistance: Not so costly after all:
“These results demonstrate how profoundly the magnitude of fitness costs associated with disease resistance may be shaped by genomic architecture and pleiotropy… These findings shed much-needed light on how the full repertoire of R genes is maintained in the A. thaliana genome. More broadly, these results show that the nature of fitness costs and trade-offs of disease resistance vary among loci even within the same host. Such information is crucial for crop breeding, where the challenge lies in producing high-yield crops while minimizing the cost of disease control.”
We illustrated this post with Sir John Tenniel’s drawing of the Red Queen and Alice from Lewis Carroll’s Through the Looking-Glass. The Red Queen tells Alice: “Now, here, you see, it takes all the running you can do, to keep in the same place”. This is commonly used as an analogy for co-evolution, as hosts and parasites have to rapidly adapt to each other in order to not loose the race. A concept introduced by Leigh Van Valen’s 1973 article. The rate of this co-evolutionary arms race is expected to be constrained by fitness costs.
Alice MacQueen performed fitness experiments as part of her doctoral dissertation and is now a post doctoral researcher with the Juenger lab in Austin Texas.
Xiaoqin Sun worked with the Bergelson lab from 2007-2009 and is now at the Institute of Botany, Jiangsu Province and Chinese Academy of Sciences, Nanjing.