Phenotypic plasticity and genotype-environment interactions (GEI) play a prominent role in plant morphological diversity and in the potential functional capacities of plant life history traits. The genetic basis of plasticity and GEI however, is poorly understood in most organisms. We used both quantitative genetic and quantitative trait locus (QTL) mapping approaches to study plasticity and GEI of inflorescence development traits in response to different photoperiods in Arabidopsis thaliana. Two sets of recombinant inbred lines (Ler x Col and Cvi x Ler) were reared under both short day (10 hour) and long day (14 hour) photoperiods. We show that plasticity and GEI are regularly observed for multiple inflorescence development traits in A. thaliana and that these phenotypic responses can be attributable (at least in part) to the variable effects of specific QTLs. Pooled across all inflorescence development traits, sixteen of 51 QTLs (31.4%) exhibited significant GEI in the Ler x Col lines and 32 of 61 QTLs (51.6%) exhibited significant GEI in the Cvi x Ler lines. QTLs exhibiting GEI were generally of two types: 1) those showing changes in magnitude of effects across photoperiod environments but not showing differences in sign of effects, and 2) those showing changes in rank order (sign) of effects across photoperiod environments. These findings provide insights into how genomes and environmental factors interact to determine phenotypes.

Key words: Arabidopsis thaliana, genotype-environment interactions, inflorescence development, QTLs, quantitative genetics