Hybrid Incompatibility in Arabidopsis Is Determined by a Multiple-Locus Genetic Network    

Abstract

O.T., R.M., T.A.)The cross between Arabidopsis thaliana and the closely related species Arabidopsis arenosa results in postzygotic hybrid incompatibility, manifested as seed death. Ecotypes of A. thaliana were tested for their ability to produce live seed when crossed to A. arenosa. The identified genetic variation was used to map quantitative trait loci (QTLs) encoded by the A. thaliana genome that affect the frequency of postzygotic lethality and the phenotypes of surviving seeds. Seven QTLs affecting the A. thaliana component of this hybrid incompatibility were identified by crossing a Columbia 3 C24 recombinant inbred line population to diploid A. arenosa pollen donors. Additional epistatic loci were identified based on their pairwise interaction with one or several of these QTLs. Epistatic interactions were detected for all seven QTLs. The two largest additive QTLs were subjected to fine-mapping, indicating the action of at least two genes in each. The topology of this network reveals a large set of minor-effect loci from the maternal genome controlling hybrid growth and viability at different developmental stages. Our study establishes a framework that will enable the identification and characterization of genes and pathways in A. thaliana responsible for hybrid lethality in the A. thaliana 3 A. arenosa interspecific cross.

Early Disruption of Maternal–Zygotic Interaction and Activation of Defense-Like Responses inArabidopsisInterspecific Crosses

“…Inactivation of this pathway either on the maternal side (TTG2) or on the filial side (IKU1) has comparable effects. However, improvement in seed survival is only partial, consistent with multilocus incompatibility where each gene contributes to a fraction of the phenotypic variance observed in the population (Burkart-Waco et al, 2012).…”

“…We compared seed development of A. thaliana ecotypes Col-0 and C24, which respectively produce 0 to 1% and ;17% live seed after interspecific hybridization to A. arenosa (Burkart-Waco et al, 2012). Photomicrographs of developing seed from A. thaliana controls and interspecific F1 hybrid seed are shown in Figure 1.…”

“…We previously identified quantitative genetic variation in seed survival between Col-0 hybrids and C24 hybrids (Burkart-Waco et al, 2012). To connect this variation and the observed differences in expression, we identified those genes differentially expressed between the two ecotypes in the 3 DAP seed and silique libraries (two replicates each).…”

“…In Arabidopsis species, there is natural variation for interspecific hybrid incompatibility, and the molecular nature of seed death remains poorly understood (Burkart-Waco et al, 2012). When Arabidopsis thaliana is crossed to its close relative Arabidopsis arenosa, abnormalities are observed in later stages of seed development (Josefsson et al, 2006;Walia et al, 2009;BurkartWaco et al, 2012).…”

“…This cross can only be performed using A. thaliana as the seed parent Bushell et al, 2003). The genetic basis of the differential response between highly incompatible A. thaliana Columbia-0 (Col-0; 0% live seed) and moderately compatible C24 (17% live seed) was mapped to seven additive and several more epistatic quantitative trait loci (QTL) (Burkart-Waco et al, 2012). The identity of these QTL and the mode of action of the genes causing incompatibility are unknown.…”