Nicotinamide adenine dinucleotide phosphate-malic enzymetype C4 pathway
The C4 photosynthesis pathway was discovered in sugarcane. We identified 24 genes for 7 key enzymes related to the nicotinamide adenine dinucleotide phosphate-malic enzyme
(NADP-ME) C4 pathway. Increased expression of core C4 enzymes played a major role in the evolution of C4 photosynthesis34. Based on gene expression and phylogenetic analysis, 8 genes—SsCA1, SsCA2, SsPEPC1, SsPEPC-k1, SsNADP-MDH2,
SsNADP-ME2, SsPPDK1 and SsPPDK-RP2—were identified as C4-type genes .A tandem duplication of SsNADP-ME2, SsNADP-ME1, also displayed a C4 expression profile similar to that of SsNADP-ME2.But the ortholog of SsNADP-ME1 in
maize, ZmNADP-ME (GRMZM2G122479), displayed non-C4-type expression, suggesting that neofunctionalization of SsNADP-ME1 for C4 in sugarcane occurred after the divergence of maize and tribe Andropogoneae.
Fig.Nicotinamide adenine dinucleotide phosphate-malic enzymetype C4 pathway
Tab.The number of putative carbon fixation genes in S. spontaneum, S. bicolor , Z.mays and O.sativa.
| Gene | S. spontaneum | S. bicolor | Z.mays | O.sativa |
| Carbonic anhydrase (CA) | 4 | 4 | 3 | 1 |
| Phosphoenolpyrvuate carboxylase (PEPC) | 5 | 5 | 5 | 5 |
| Phosphoenolpyruvate carboxylase kinase (PEPCK) | 3 | 3 | 3 | 3 |
| Malate dehydrogenase (MDH) | 2 | 2 | 1 | 1 |
| Malic enzyme (ME) | 5 | 5 | 5 | 4 |
| Pyruvate phosphate dikinase (PPDK) | 2 | 2 | 2 | 2 |
| PPDK regulatory protein (RP) | 3 | 3 | 2 | 1 |
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2.Comparison of C4-type genes between S. spontaneum and Sorghum