Good!!!

But wouldn't that be better to go for the tryptophan decarboxylase from rice seedlings, like this Conversion of 5-hydroxytryptophan into serotonin by tryptophan decarboxylase in plants, Escherichia coli, and yeast - PubMed ? That's basically a good deal of the work already done and characterised. The plasmid can already be acquired by the group that made this research. I truly do not worry much about this part,

INMT is the pain. Cloning from rabbit, rat, mouse lung is the most straightforward, but as the paper you  mentioned describes, INMT is inhibited by its end product, dmt. But this is the most promising way to go; first, even if you get a small amount of dmt produced then you proved your "proof of principle" and then you have a system you can tweak to perfection. Second, you have no idea about INMT from phalaris or other plants, genome resources are scarce and there's not much you can do (unless you enjoy constructing a phalaris library, fish out plant INMT homologues just to find out they do not do what you like...) The methyltransferases in plants that do this type of job are pretty much uncharacterised to hypothetical.

My first bet would therefore be on the lung INMT, unless someone has better candidates. We'll also need to tag it somehow to be able to detect it in western blots. Same goes for TDC.

Are you still