Cytochrome P450 monooxygenases (P450s) catalyze a wide variety of monooxygenation reactions in primary and secondary metabolism in plants. The share of P450 genes in each plant genome is estimated to be up to 1%. This implies that the diversification of P450 has made a significant contribution to the ability to acquire the emergence of new metabolic pathways during land plant evolution. The P450 families conserved universally in land plants contribute to their chemical defense mechanisms. Several P450s are involved in the biosynthesis and catabolism of plant hormones. Species-specific P450 families are essential for the biosynthetic pathways of phytochemicals such as terpenoids and alkaloids. Genome wide analysis of the gene clusters including P450 genes will provide a clue to defining the metabolic roles of orphan P450s. Metabolic engineering with plant P450s is an important technology for large-scale production of valuable phytochemicals such as medicines.Key words P450; metabolic engineering; terpenoid; phytohormone
P450S IN THE PLANT KINGDOMMore than 5000 sequences have been stored in a plant P450 database.1) The number of P450 genes in Arabidopsis (Arabidopsis thaliana) is 245, and P450 is the third biggest family gene in Arabidopsis.1) The numbers of P450 genes in several other plants are 316 in grapevine (Vitis vinifera), 332 in soybean (Glycine max), 312 in poplar (Populus trichocarpa), 334 in rice (Oryza sativa), and 372 in sorghum (Sorghum bicolor), which are estimated to represent up to 1% of the total gene annotations of each plant species .2,3) Transcriptome analyses are also contributing to the vast increase in identified P450 sequences from various plant species (http://compbio.dfci. harvard.edu/tgi/plant.html). However, the functions of most of these are still unknown. For instance, in Arabidopsis, the number of functionally characterized P450 genes is about 60, which means that more than 70% of its 245 P450 genes still remain to be characterized.
4)Plant P450s have been shown to participate in a variety of biochemical pathways to produce primary and secondary metabolites such as phenylpropanoids, alkaloids, terpenoids, lipids, cyanogenic glycosides, and glucosinolates, as well as plant hormones.4) The diversification of P450 has had a significant biochemical impact on the emergence of new metabolic pathways during the evolutionary process of land plants.
DIVERSIFICATION OF P450 GENES IN LAND PLANTSThe driving force of plant P450 diversification is closely linked to the survival strategy of land plants, conferring advantages in the continuous evolutionary competition and mutualism with other organisms. The role of plant P450 can be discussed in relation to the following categorized reactions and metabolisms: category I, essential reactions conserved in the plant kingdom; category II, core metabolisms conserved in all land plants; category III, essential metabolisms which emerged during the evolution of flowering plants (e.g., plant hormone homeostasis); category IV, secondary metabolisms unique t...