Table 1.

Summary of the different traits associated with NAD-ME and NADP-ME subtypes.

Traits	Description	NAD-ME	NADP-ME	Reference
Evolutionary scenario	Recruitment of NAD-ME or NADP-ME from C3 ancestor	NAD-ME comes from existed mitochondrial NAD-ME; dual performance in C4 photosynthesis and all cells	NADP-ME arises from gene duplication from C3 ancestor; specific function in C4 photosynthesis	Maier et al., 2011
Physiology		Higher water use efficiency (?)	Higher photosynthetic nitrogen use efficiency	Ghannoum, 2005; Pinto et al., 2014, 2015
Kranz anatomy	Chloroplast position in BS cells	Centrifugal	Centripetal in monocot centrifugal in dicot	Lundgren et al., 2014
	Grana in BS chloroplasts	Developed	Reduced
	Inner layer of bundle sheath in BS cells	Double sheath (mestome sheath and vascular bundle)	Single sheath (vascular bundle)
	The origination of cell division	BS and M derived from the ground meristem; the mestome sheath derived from the procambium	BS derived from the procambium; M cells derived from ground meristem	Soros and Dengler, 2001
C4 biochemical cycle	Enzymes and site of decarboxylation	NAD-malic enzyme in mitochondrion	NADP-malic enzyme in chloroplast	Furbank, 2011; Gowik and Westhoff, 2011; Pick et al., 2011
	Decarboxylated acid	Aspartate/alanine	Malate/pyruvate Aspartate/alanine (?)
C4 plastid transporters	Pyruvate transport in chloroplasts of M cells	Sodium:pyruvate cotransporters	Proton:pyruvate cotransporters in monocots	Weber and von Caemmerer, 2010; Brautigam et al., 2011; Furumoto et al., 2011
	Transporters in mitochondrion of BS cells	Required	N/A
	CO2 transport in chloroplasts of BS cells	Required	N/A
M and BS cell-specific function	PSII activity in BS cells	Enhanced	Reduced	Meierhoff and Westhoff, 1993
	C4 acid decarboxylation and assimilation	Light-dependent; sufficient supply of ribulose-1,5-diphosphate in Calvin cycle	Partially light-dependent; insufficient supply of ribulose-1,5-diphosphate in Calvin cycle	Hatch and Kagawa, 1976
	Cell type-gene enrichment	RNA regulation enhanced or equally distributed in M cells; protein biogenesis enhanced or equally distributed in BS cells	RNA regulation enhanced in BS cells; protein biogenesis enhanced in M cells	Chang et al., 2012; Aubry et al., 2014, John et al., 2014; Rao et al., 2016

The statements remaining in argument are indicated with question marks. BS, bundles sheath; M, mesophyll; N/A, not applied.