The meta-hydroxylation step in the phenylpropanoid pathway: a new level of complexity in the pathway and its regulation

Abstract

Together in silico and genetic mining approaches have recently designated the CYP98 family of plant cytochromes P450 as the family of enzymes that catalyzes the meta-hydroxylation step in the phenylpropanoid pathway. This meta-hydroxylation is not catalyzed on the free p-coumaric acid as anticipated, but on its conjugates with shikimic, quinic, or phenyllactic acids. While all CYP98s have in common phenol meta-hydroxylase activity, pcoumaroylshikimate remains their preferred substrate. High expression of CYP98s is detected in lignifying tissues in stems, roots, and siliques. The CYP98A3 gene disruption in Arabidopsis thaliana leads to a drastic inhibition of lignin synthesis, cell growth, and plant development. The metahydroxylation of phenolic precursors is thus essential for higher plant development.

Protein–Protein and Protein–Membrane Associations in the Lignin Pathway

“…The most consistently high FRET values were observed for the couple CYP98A3-HCT. This is in agreement with the following facts: (1) HCT is found associated with the membrane and readily relocalizes to the ER upon coexpression of CYP98A3, (2) HCT is both the donor of substrate and acceptor of product of CYP98A3 (Hoffmann et al, 2003), and (3) the shikimate conjugates of p-coumaric and caffeic acid that are the metabolic intermediates between the two enzymes are usually not detected in tissues of wild-type Arabidopsis (Schoch et al, 2006). The latter observation implies a tight coupling between CYP98A3 and HCT that might require close enzyme association.…”

“…Together, C39H and HCT form a loop sequence at the branch point to lignin synthesis (Schoch et al, 2001;Hoffmann et al, 2004). The two enzymes seem to be tightly coupled since shikimate derivatives never accumulate to UV-detectable levels in wildtype nor in C39H-null mutant plants (Schoch et al, 2006).…”

Isolation and mapping of a C3′H gene (CYP98A49) from globe artichoke, and its expression upon UV-C stress

“…The 3 0 -hydroxylation step is critical in the synthesis of phenolic compounds. Most of the members of the CYP98 family, described to date, metabolize shikimate esters of p-coumaric acid more efficiently than quinate esters (Schoch et al 2001(Schoch et al , 2006Morant et al 2007). On the other hand CYP98A35 from coffee is capable of metabolizing p-coumaroylquinate and p-coumaroylshikimate with the same efficiency (Mahesh et al 2007).…”

“…The 3 0 -hydroxylation of the phenylpropanoid ring is essential not only for the synthesis of lignin (Franke et al 2002;Abdulrazzak et al 2006;Chen and Dixon 2007), but is also an important step in the synthesis of chlorogenic acid (Schoch et al 2006;Mahesh et al 2007). The CYP98 family of plant cytochromes P450 has been designated as the family of enzyme that performs the meta-hydroxylation step in the phenylpropanoid pathway ( Fig.…”

“…1). This meta-hydroxylation is not catalyzed on free p-coumaric acid, but on its conjugates with shikimic, quinic or phenyllactic acids (Schoch et al 2006). The protein and encoding genes in this family are also referred to as C3 0 H.…”