Phytochrome interacting factor (PIF) transcription factors have been shown to be important in the regulation of seed dormancy and germination by environmental cues. Many PIF-family transcription factors are expressed in seeds but only PIF1 and SPATULA (SPT) have been tested for a role in germination control. Here we show that PIF6 is expressed strongly during seed development, and that two splice variants exist, one full length (the alpha form), and a second, the beta form, in which a cryptic intron containing the potential DNA binding domain is spliced out, predicted to lead to the generation of a premature stop codon. Loss of PIF6 increases primary seed dormancy, whereas overexpression of the beta form, but not the alpha form, reduce dormancy. Our data show the potential for natural splice variants of PIF transcription factors to be important in the evolution of the control of environmental signalling in plants.