In Arabidopsis thaliana Heterosis Level Varies among Individuals in an F₁ Hybrid Population

Heterosis or hybrid vigour is a phenomenon in which hybrid progeny exhibit superior yield and biomass to parental lines and has been used to breed F₁ hybrid cultivars in many crops. A similar level of heterosis in all F₁ individuals is expected as they are genetically identical. However, we found variation of rosette size in individual F₁ plants from a cross between C24 and Columbia-0 accessions of Arabidopsis thaliana. Big sized F₁ plants had 26.1% larger leaf area in the 1^st and 2^nd leaves than medium sized F₁ plants at 14 days after sowing in spite of the identical genetic background. We identified differentially expressed genes between big and medium sized F₁ plants by microarray; genes involved in the category of stress response were overrepresented. We made transgenic plants overexpressing 21 genes, which were differentially expressed between the two size classes, some lines had increased plant size at 14 or 21 days after sowing but not at all time points. Change of expression levels in stress responsive genes among individual F₁ plants, implying epigenetic changes, could generate the variation in plant size of individual F₁ plants in A. thaliana.