Table 1.

Characteristics of four-carbon organic acid decarboxylating enzymes in the leaves of C₄ plants and the orthologous gene products from C₃ species.

Enzyme	Location / function in C3 leaf cells	Location / function of C4 isoforms in bundle-sheath cells	Identified changes in the genes encoding C4-associated isoforms / species (reference)	Identified differences in C4 isoforms / species (reference)
NADP-ME	Cytosol/defense, development, stress response Chloroplasts / lipid and protein biosynthesis, nitrogen assimilation, defense responses	Chloroplasts / major decarboxylase in NADP-ME-type C4 species	High BS-specific expression controlled by sequences in the upstream region, 5′-coding and 3′-UTR / Flaveria bidentis (Marshall et al., 1997; Ali and Taylor, 2001) High BS-specific expression controlled by sequences in the upstream region / Flaveria trinervia (Lai et al., 2002)	Malate inhibition / Zea mays; Sorghum bicolor (Detarsio et al., 2007; Saigo et al., 2013) Redox modulation / Zea mays; Sorghum bicolor (Alvarez et al., 2012; Saigo et al., 2013) Tetramerization / Zea mays; Sorghum bicolor (Detarsio et al., 2007; Saigo et al., 2013)
NAD-ME	Mitochondria / respiration of malate	Mitochondria / major decarboxylase in NAD-ME-type C4 species	Sequences at 5′-end of coding region responsible for BS-specific expression / Gynandropsis gynandra (Brown et al., 2011)	None identified
PCK	Cytosol / gluconeogenesis, seedling development, stomatal control, replenishment of TCA intermediates, nitrogen metabolism, pH regulation	Cytosol / major decarboxylase in PCK-type C4 species	None identified	None identified

BS, bundle-sheath; n/a, not applicable; NAD-ME, NAD-malic enzyme; NADP-ME, NADP-malic enzyme; PCK, phosphoenolpyruvate carboxykinase; UTR, untranslated region.