Table 2.

Relationship between Symbiont Gene Content and Bacteriocyte Expression of Host Gene(S) Coding the Equivalent Reactions

Symbiosis	Amino Acids
	Branched Chain Amino Acidsa		Phenylalanineb		Isoleucinec			Arginined
	Symbiont	Host	Symbiont	Host	Symbiont	Host	Host	Symbiont	Host	Host	Host
	ilvE	BCAT	tyrB	GOT	ilvA	TD	CGL	argABCDE	PCD	PRODH	OAT
Whitefly (Bemisia tabaci/Portiera)	0	+	0	+	+	+	+	0	+	+	+
Mealybug (Planococcus citri/Tremblaya+Moranella)	0	+	0	+	0		+	0	?	?	+
Psyllid (Pachypsylla venusta/Carsonella)	+	?	0	+	0	+	+	0			+
Aphid (Acyrthosiphon pisum/Buchnera)	0	+	0	+	0		+	+		+	+

Note.—Symbiont: gene present (+) or absent (0); host: abundant or enriched transcript in bacteriocytes (+); blank cell, no information.

^aThe final reaction in the synthesis of branched chain amino acids mediated by IlvE or BCAT (branched chain amino acid transaminase, which generally functions as the first reaction in BCA degradation but is reversible).

^bThe final reaction in phenylalanine synthesis mediated by the bacterial TyrB and also by host transaminases, notably aspartate transaminase (GOT, glutamate-oxaloacetate transaminase).

^cThe first reaction in the isoleucine synthesis, producing 2-oxobutanoate from the substrate threonine (bacterial IlvA and host TD) or homoserine (host CGL). IlvN, coding the second reaction in isoleucine synthesis, is also missing from the symbionts of the mealybug symbiosis, and it is unknown how this reaction may be mediated.

^dSynthesis of ornithine, an intermediate in arginine synthesis, from glutamate by the bacterial argABCDE or host PCD (1-pyrroline-5-carboxylate dehydrogenase) and OAT (ornithine aminotransferase), or from proline by the host PRODH (proline dehydrogenase), PCD and OAT.