Cuscuta form and function-evolutionary implications of its bizarre development

Abstract

During its evolution from an autotrophic ancestor, parasitic Cuscuta has lost roots, cotyledons, expanded green leaf, and cambium and has gained haustorium and heterotrophy. Though the expression of thousands of genes is expected to be permanently altered during this transformation, the extensive morphological alterations resulting from certain Single gene mutations in plants suggest that evolutionary alterations in just a few higher order regulatory genes acting either early in embryogenesis or at 'developmental forks' may have sufficed to initiate the change. Possible turning points and candidate genes associated with loss of organs and functions are identified based on similar effects in other plants. The suspected homology between root and haustorium, suggested by ontogenetic and hormonal considerations, can now be directly tested by modern recombinant DNA methods.