>Jan, does plumbagin elaboration indicate a shared codon in the caryophyllid
>clade which is *not* located on rbcL?
Certainly. I.e. it indicates a shared gene/genes in this "extended
caryophyllid" (note the quotes, this one is rather difficult to swallow for
the conservative taxonomist!) clade apparently independent from rbcL.
rbcL (ribulose bisphosphate carboxylase, L subunit) codes for a protein
involved in the process of carbon fixation coupled to photosynthesis, i.e.
a reaction in the primary metabolism of the chloroplast.
Plumbagin synthesis via the acetate-polymalonate (polyketide) pathway (in
our case presumably converting one molecule of Acetyl-CoA and five
molecules of Malonyl-CoA to one molecule of plumbagin etc.) is catalyzed by
(a yet unknown) polyketide synthase (pks), rather rare in this form in
plants (a chemically comparable more widespread reaction being flavonoid
biosynthesis, but here only part of the molecule is the product of a pks
reaction), i.e. a reaction in the secondary metabolism.
Polygonaceae (which lack a priori plumbagin formation) frequently contain
biosynthetically related anthraquinones. So the possession of pks (or
rather a special pks protein family) seems to be a peculiar feature of all
the families from Polygonaceae to Nepenthaceae and Droseraceae.
Kind regards
Jan