Epistasis for Fitness-Related Quantitative Traits in Arabidopsis thaliana

Russell Malmberg at the University of Georgia has published a new paper in Genetics on epistasis in Arabidopsis.

Malmberg RL, Held S, Waits A, Mauricio R. Epistasis for Fitness-Related Quantitative Traits in Arabidopsis thaliana Grown in the Field and in the Greenhouse. Genetics. 2005 Sep 12 [PubMed]

Abstract:

The extent to which epistasis contributes to adaptation, population differentiation, and speciation is a long-standing and important problem in evolutionary genetics. Using recombinant inbred lines of Arabidopsis thaliana grown under natural field conditions, we have examined the genetic architecture of fitness-correlated traits with respect to epistasis; we identified both single locus additive and two locus epistatic QTLs for natural variation in fruit number, germination, and seed length and width. For fruit number, we found 7 significant epistatic interactions, but only 2 additive QTLs. For seed germination, length, and width, there were from 2 to 4 additive QTLs and 5-8 epistatic interactions. The epistatic interactions were both positive and negative. In each case, the magnitude of the epistatic effects were roughly double those of the effects of the additive QTLS, varying from -41% to +29% for fruit number, and from -5% to +4% for seed germination, length, and width. A number of the QTLs we describe participate in more than one epistatic interaction, and some loci identified as additive also may participate in an epistatic interaction; the genetic architecture for fitness traits may be a network of additive and epistatic effects. We compared the map positions of the additive and epistatic QTLs for germination, seed width, and seed length from plants grown in both the field and greenhouse. While the total number of significant additive and epistatic QTLs was similar between the two growth conditions, the map locations were largely different. We found a small number of significant epistatic QTL x environment effects when we tested directly for them. Our results support the idea that epistatic interactions are an important part of natural genetic variation, and reinforce the need for caution in comparing results from greenhouse-grown and field-grown plants.