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The Promoter for C₄-type Mitochondrial Aspartate Aminotransferase Does not Direct Bundle Sheath-specific Expression in Transgenic Rice Plants

Nomura, Mika, Higuchi, Tomonori, Katayama, Kenichi, Taniguchi, Mitsutaka, Miyao-Tokutomi, Mitsue, Matsuoka, Makoto, Tajima, Shigeyuki
Plant & cell physiology 2005 v.46 no.5 pp. 743-753
Panicum miliaceum, C4 photosynthesis, C4 plants, mitochondria, cytosol, plant proteins, aspartate transaminase, isozymes, promoter regions, transgenes, recombinant fusion proteins, beta-glucuronidase, reporter genes, gene expression regulation, Oryza sativa, rice, grain crops, transgenic plants, bundle sheath cells, light, plant biochemistry, plant genetics, nucleotide sequences
For NAD-malic enzyme (NAD-ME)-type C₄ photosynthesis, two types of aspartate aminotransferase (AAT) are involved. We examined the expression pattern of the Panicum miliaceum mitochondrial Aat gene (PmAat) and P. miliaceum cytosolic Aat gene (PcAat) in transgenic rice plants, which were specifically expressed in bundle sheath cells (BSCs) and mesophyll cells (MCs), respectively. Expression of a {szligbeta}-glucuronidase (GUS) reporter gene under the control of the PcAat promoter was regulated in an organ-preferential and light-dependent manner in the transgenic rice plants. However, the PmAat promoter drove the GUS expression in all organs we tested without light dependency, and this non-preferential expression pattern was also observed in transgenic rice with introduction of the intact PmAat gene. The expression patterns of the rice counterpart Aat genes to PmAat or PcAat showed that the rice mitochondrial Aat (RmAat1) gene was expressed in all organs tested in a light-independent manner, while expression of the rice cytosolic Aat (RcAat1) gene showed an organ-preferential and light-dependent pattern. Taking these results together, we can generalize that the regulatory system of BSC-specific or light-dependent expression of mitochondrial Aat is not shared between P. miliaceum (C₄) and rice (C₃) and that the expression of the C₄ genes introduced into rice mimics that of their counterpart genes in rice.