Dose-dependent interactions between two loci trigger altered shoot growth in BG-5 × Krotzenburg-0 (Kro-0) hybrids of Arabidopsis thaliana.

Hybrids occasionally exhibit genetic interactions resulting in reduced fitness in comparison to their parents. Studies of Arabidopsis thaliana have highlighted the role of immune conflicts, but less is known about the role of other factors in hybrid incompatibility in plants. Here, we present a new hybrid incompatibility phenomenon in this species. We have characterized a new case of F1 hybrid incompatibility from a cross between the A. thaliana accessions Krotzenburg-0 (Kro-0) and BG-5, by conducting transcript, metabolite and hormone analyses, and identified the causal loci through genetic mapping. The F1 hybrids showed arrested growth of the main stem, altered shoot architecture, and altered concentrations of hormones in comparison to parents. The F1 phenotype could be rescued in a developmental-stage-dependent manner by shifting to a higher growth temperature. These F1 phenotypes were linked to two loci, one on chromosome 2 and one on chromosome 3. The F2 generation segregated plants with more severe phenotypes which were linked to the same loci as those in the F1 . This study provides novel insights into how previously unknown mechanisms controlling shoot branching and stem growth can result in hybrid incompatibility.