Plant cytochromes P450 (P450s) catalyze a wide variety of
monooxygenation/hydroxylation reactions in primary and secondary
metabolism. The number of P450 genes in plant genomes is estimated
to be up to 1% of total gene annotations of each plant species. This implies
that diversification within P450 gene superfamilies has led to the
emergence of new metabolic pathways throughout land plant evolution.
The conserved P450 families contribute to chemical defense mechanisms
under terrestrial conditions and several are involved in hormone
biosynthesis and catabolism. Species-specific P450 families are essential
for the biosynthetic pathways of species-specialized metabolites. Future
genome-wide analyses of P450 gene clusters and coexpression networks
should help both in identifying the functions of many orphan P450s and
in understanding the evolution of this versatile group of enzymes.