Table 1.

Heterologous expression yields of plant PPOs per litre of culture.

Plant PPO	yield	reference
PPO (M. domestica cv Fuji)	inactive protein	31
PPOs (Trifolium pratense)	insoluble protein	30
PPOs (Camelia sinensis)	insoluble protein	23
PPO-6 (Taraxacum officinale)	0.5–2 mg	32
PPO-2 (Taraxacum officinale)	8.7 ± 2.9 mg	33
cgAUS1 (Coreopsis grandiflora)	5–6 mg	34
MdPPO1	225 mg	this work
MdPPO2	60.0 mg	this work
MdPPO3	26.5 mg	this work