Elevated Expression of PGR5 and NDH-H in Bundle Sheath Chloroplasts in C4 Flaveria Species

Cyclic electron transport around PSI has been proposed to supply the additional ATP required for C-4 photosynthesis. To investigate the nature of cyclic electron pathways involved in C-4 photosynthesis, we analyzed tissue-specific expression of PGR5 (PROTON GRADIENT REGULATION 5), which is involved in the antimycin A-sensitive pathway, and NDH-H, a subunit of the plastidial NAD(P)H dehydrogenase complex, in four Flaveria species comprising NADP-malic enzyme (ME)-type C-4, C3C4 intermediate and C-3 species. PGR5 was highly expressed in the C-4 species and enriched in bundle sheath chloroplasts together with NDH-H, suggesting that electron transport of both PGR5-dependent and NDH-dependent cyclic pathways is promoted to drive C-4 photosynthesis.