TISSUE-SPECIFIC AND LIGHT-MEDIATED EXPRESSION OF THE C-4 PHOTOSYNTHETIC NAD-DEPENDENT MALIC ENZYME OF AMARANTH MITOCHONDRIA

In the C-4 dicotyledonous grain plant amaranth (Amaranthus hypochondri acus), a mitochondrial NAD-dependent malic enzyme (NAD-ME; EC 1.1.1.39 ) serves a specialized and essential role in photosynthetic carbon fix ation. In this study we have examined specialized photosynthetic gene expression patterns for the NAD-ME alpha subunit. We show here that th e alpha subunit gene is preferentially expressed in leaves and cotyled ons (the most photosynthetically active tissues), and this expression is specific to the bundle-sheath cells of these tissues from the earli est stages of development. Synthesis of the alpha subunit polypeptide and accumulation of its corresponding mRNA are strongly light-dependen t, but this regulation is also influenced by seedling development. In addition, light-dependent accumulation of the alpha subunit mRNA is re gulated at transcriptional as well as posttranscriptional levels. Our findings demonstrate that the NAD-ME of amaranth has acquired numerous complex tissue-specific and light-mediated regulation patterns that d efine its specialized function as a key enzyme in the C-4 photosynthet ic pathway.