Cytochrome P450 enzymes in the phenylpropanoid pathway: CYP73 and CYP98 candidate genes in Chara braunii, Anthoceros agrestis, Marchantia polymorpha and Physcomitrium patens.

CYP73 and CYP98 are two cytochrome P450 monooxygenase families present in bryophytes and tracheophytes, and they play key roles in the formation of phenolic compounds containing a caffeic acid moiety and more complex phenolic compounds. CYP73 encodes the second enzyme in the core phenylpropanoid pathway and is the first enzyme family in this pathway so far exclusively found in land plants and not in any water-living sister clades, like the streptophyte algae. That makes CYP73 a prime candidate for investigations into necessary adaptations during terrestrialization. This study aims to support our knowledge on the evolution of this pathway by characterizing the enzymes translated from (putative) CYP73 genes from the bryophytes Anthoceros agrestis, Marchantia polymorpha, and Physcomitrium patens and CYP98 genes from Marchantia polymorpha and Physcomitrium patens. Furthermore, this insight into the function of bryophyte CYP73 informed a more specific search for potential CYP73 candidates in the streptophyte alga Chara braunii. The possibility that land plant CYP73 activity originated in streptophyte algae would be greatly supported if rudimentary CYP73 activity could be found in native Chara candidate genes or induced by slight mutations in inactive Chara enzymes. However, no such mutation led to product formation by enzymes encoded by Chara braunii candidate genes. The bryophyte CYP98 enzymes prefer 4-coumaroyl amides as substrates, though 4-coumaroyl esters are generally the common substrates of tracheophyte CYP98 enzymes. This shows a major difference in functionality. Thus, this study provides a comparative characterization of CYP genes from model bryophytes that are canonically associated with phenylpropanoid metabolism.