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.

Novel allelic variants in ACD6 cause hybrid necrosis in local collection of Arabidopsis thaliana.

Hybrid necrosis is a common type of hybrid incompatibility in plants. This phenomenon is caused by deleterious epistatic interactions, resulting in spontaneous activation of plant defenses associated with leaf necrosis, stunted growth and reduced fertility in hybrids. Specific combinations of alleles of ACCELERATED CELL DEATH 6 (ACD6) have been shown to be a common cause of hybrid necrosis in Arabidopsis thaliana. Increased ACD6 activity confers broad-spectrum resistance against biotrophic pathogens but reduces biomass production. We generated 996 crosses among individuals derived from a single collection area around Tübingen (Germany) and screened them for hybrid necrosis. Necrotic hybrids were further investigated by genetic linkage, amiRNA silencing, genomic complementation and metabolic profiling. Restriction site associated DNA (RAD)-sequencing was used to understand genetic diversity in the collection sites containing necrosis-inducing alleles. Novel combinations of ACD6 alleles found in neighbouring stands were found to activate the A. thaliana immune system. In contrast to what we observed in controlled conditions, necrotic hybrids did not show reduced fitness in the field. Metabolic profiling revealed changes associated with the activation of the immune system in ACD6-dependent hybrid necrosis. This study expands our current understanding of the active role of ACD6 in mediating trade-offs between defense responses and growth in A.  thaliana.