LAUSR

Inactive auxin conjugates are accumulated in plants and hydrolyzed to recover phytohormone action. A family of metallopeptidase orthologues has been conserved in Plantae to help regulate auxin homeostatic levels during growth and development. This hydrolase family was recently traced back to liverwort, the most ancient extant land plant lineage. Liverwort’s auxin hydrolase has little activity against auxin conjugate substrates and does not appear to actively regulate auxin. This finding, along with data that shows moss can synthesize auxin conjugates, led to examining another bryophyte lineage, Physcomitrella patens. We have identified and isolated three M20D hydrolase paralogues from moss. The isolated enzymes strongly recognize and cleave a variety of auxin conjugates, including those of indole butyric and indole propionic acids. These P. patens hydrolases not only appear to be “cryptic”, but they are likely to have derived from soil bacteria through Horizontal Gene Transfer. Additionally, support is presented that the plant-type M20D peptidase family may have been universally lost from mosses after divergence from the common ancestor with liverwort.