User:Trorstad/Cytochrome p450

Plants
Plant Cytochrome P450 plays an important role in plant defense– involvement in phytoalexin biosynthesis, hormone metabolism, and biosynthesis of other secondary metabolites. The expression of cytochrome p450 genes are regulated in response to environmental stresses which is why they play an important role in plant defense mechanisms.

Phytoalexins are very important in plant defense mechanisms as they are antimicrobial compounds produced by plants in response to plant pathogens. Phytoalexins are not pathogen specific, but rather plant specific; each plant has their own unique set of phytoalexins. Even though phytoalexins aren’t pathogen specific, they can still attack a wide range of different pathogens. Arabidopsis is a plant closely related to cabbage and mustard with the phytoalexin Camelaxin. Camelaxin originates from tryptophan and its biosynthesis involves five cytochrome P450 enzymes. The five cytochrome P450 enzymes include CYP79B2, CYP79B3, CYP71A12, CYP71A13 and CYP71B15. The first step of camelaxin biosynthesis from tryptophan to indole-3-acetaldoxime (IAOx) is catalyzed by CYP79B2 or CYP79B3. The conversion of IAOx is then immediately converted to indole-3-acetponitrile (IAN) and this conversion is controlled by CYP71A13 or its homolog CYP71A12. The last two steps of the biosynthesis pathway of camelaxin is catalyzed by CYP71B15. In this step, indole-3-carboxylic acid (DHCA) is formed from cysteine-indole-3-acetonitrile (Cys(IAN)) followed by the biosynthesis of camelaxin. There are some intermediate steps within the pathway that remain unclear, but it is well understood that cytochrome P450 is pivotal in camelaxin biosynthesis and that this phytoalexin plays a major role in plant defense mechanisms.

Furthermore, Cytochrome P450s are largely responsible for the synthesis of the jasmonic acid (JA) (one of the biggest hormonal defenses against abiotic and biotic stresses for plant cells.) For example, a P450, CYP74A is involved in the dehydration reaction to produce an insatiable allene oxide from hydroperoxide. This chemical reaction is critical in biotic stresses that can be caused by plant wounding. Furthermore, several CYP94s (CYP94C1 and CYP94B3) are related to JA-Ile turnover and show that JA-Ile oxidation status impacts plant signaling in a catabolic manner. Cytochrome P450 hormonal regulation in response to extracellular and intracellular stresses is critical for proper plant defense response.

Plant cytochrome P450s are involved in a wide range of biosynthetic reactions and target a diverse range of biomolecules. These reactions lead to various fatty acid conjugates, plant hormones, secondary metabolites, lignins, and a variety of defensive compounds. Plant genome annotations suggest that cytochrome P450 genes make up as much as 1% of the plant genes. The number and diversity of P450 genes is responsible, in part, for the multitude of bioactive compounds.

Cytochrome P450 aromatic O-demethylase, which is made of two distinct promiscuous parts: a cytochrome P450 protein (GcoA) and three domain reductase, is significant for its ability to convert Lignin, the aromatic biopolymer common in plant cell walls, into renewable carbon chains in a catabolic set of reactions. In short, it is a facilitator of a critical step in Lignin conversion.