Transcription Factors and Darwin's 'Abominable Mystery': Positive Autoregulation in Floral Zygomorphy

摘要

The Cretaceous was a great time for angiosperms; so great that Darwin himself identified the dramatic increase in the number of angiosperm species as an 揳bominable mystery?(reviewed in Friedman, 2009). Trying to explain the astonishing explosion of angiosperm diversity gave Darwin such trouble that he even toyed with the idea of a lost continent where angiosperms had diversified off the (fossil) record. However, he also landed on another, more likely, explanation: the interaction between plants and insects. Indeed, one key evolutionary innovation that appeared in some major lineages at this time was a change in floral symmetry, from radially symmetrical actinomorphic flowers to bilaterally symmetrical zygomorphic flowers. The morphological diversity of zygomorphic flowers allows more specific interactions with pollinators with bilateral vision, such as insects; this interaction may drive speciation by facilitating reproductive isolation.