Abstract
C4 plants have two types of photosynthetic cells, mesophyll (MC) and bundle sheath cells (BSC), that possess developed chloroplasts. Active metabolite transport is conducted across the chloroplast envelope membranes. We previously reported that chloroplastic 2-oxoglutarate/malate transporter (OMT) of maize, an NADP-ME-type C4 plant, is abundantly expressed in MC of leaf blades but not in BSC and root tissues. In this study, we investigated the cell-specific expression of OMT genes in other C4-type plants and its nitrogen-responsiveness. The expression of OMT in sorghum (NADP-ME-type), finger millet, proso millet (NAD-ME-type), rhodes grass and guinea grass (PCK-type) was MC-specific. The abundant expression of OMT in leaf blades was also confirmed in sorghum, finger millet and rhodes grass. Furthermore, the transcripts of OMT in maize leaf blades accumulated more rapidly in response to the nitrate supplementation compared to ammonium. Together with these results, there is a possibility that the common function of MC-specific OMT is supply of stromal reducing equivalents to cytosolic nitrate reductase.
