Academic journal article Genetics

Complex Epistasis for Dobzhansky-Muller Hybrid Incompatibility in Solanum

Academic journal article Genetics

Complex Epistasis for Dobzhansky-Muller Hybrid Incompatibility in Solanum

Article excerpt

ABSTRACT

We examined the prevalence of interactions between pairs of short chromosomal regions from one species (Solanum habrochaites) co-introgressed into a heterospecific genetic background (Solanum lycopersicum). Of 105 double introgression line (DIL) families generated from a complete diallele combination of 15 chromosomal segments, 39 (~38%) showed evidence for complex epistasis in the form of genotypic and/or allelic marker transmission distortion in DIL F^sub 2^ populations.

INTRINSIC postzygotic isolation (environment-independent hybrid inviability and sterility) is often due to deleterious genetic interactions between loci that have functionally diverged during the evolution of new species [i.e., "Dobzhansky-Muller" incompatibilities (DMIs)] (COYNE and ORR 2004). Most standard models of this process assume that individual DMIs are due to pairwise genetic interactions (one in each diverging lineage) and that each DMI contributes additively to the expression of hybrid incompatibility between diverging species (some models can relax the first assumption; TURELLI and ORR 2000; ORR and TURELLI 2001; WELCH 2004). Nonetheless, if interspecific epistasis is more complex, there could be important consequences for the temporal accumulation of species barriers, and the number of loci required to complete speciation (TURELLI et al. 2001; KONDRASHOV 2003; WELCH 2004). For example, if epistasis between different conspecific loci is generally synergistic (i.e., if the combined effect of two conspecific loci is greater than expected on the basis of their individual effects on hybrid incompatibility), fewer DMIs will be required for the expression of complete reproductive isolation, with a correspondingly shorter time to speciation. [Conceptually similar expectations were first developed in the context of the epistasis among deleterious recessive loci causing inbreeding depression (KONDRASHOV 1984).] Epistasis amongmore than two loci, therefore, could be fundamentally important in determining patterns and rates of evolution of isolation between diverging species. Nonetheless, the prevalence and nature of interactions between more than two loci from one or both species involved in a hybridization (i.e., "complex epistasis"), and their effects on hybrid incompatibility, is poorly understood empirically.

The goal of this study was to assess evidence for genetic interactions between different chromosomal regions from one species when introgressed together pairwise in the background of a second species (Figure 1). Genetic interactions influencing hybrid incompatibility were detected by measuring the degree to which the genetic composition of F^sub 2^ populations deviated from Mendelian expectations [i.e., transmission ratio distortion (TRD)]. We selected 15 chromosomal regions for inclusion in the study (Table 1), drawing from a set of near-isogenic lines (NILs) previously developed between two plant species in the genus Solanumsection Lycopersicon (the tomato clade). Each NIL contains a unique short chromosomal region from the wild species Solanum habrochaites (SH) introgressed into the otherwise isogenic genetic background of the domesticated tomato, S. lycopersicum (SL) (MONFORTE and TANKSLEY 2000; see also MOYLE and GRAHAM 2005 for a previous summary). Note that some of the NILs used here are known to contain QTL for hybrid incompatibility that acts at later stages of development (partial pollen and/or seed sterility); however, the detection of TRD at early postzygotic embryonic stages in this study appears to be unrelated to whether one or both introgressions contain loci for these later acting incompatibilities (see Table 1 and below).

To generate lines with two introgressed regions [double introgression lines (DILs)], a complete diallele cross was performed to combine each introgression with every other introgression (Figure 1), for a total of 105 unique pairwise combinations of the 15 regions. In one of the NIL-NIL combinations, no crosses produced viable seed despite being performed at least 20 times using both reciprocal directions. …

Search by... Author
Show... All Results Primary Sources Peer-reviewed

Oops!

An unknown error has occurred. Please click the button below to reload the page. If the problem persists, please try again in a little while.