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

Abstract

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 beta-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.

An Untranslated cis-Element Regulates the Accumulation of Multiple C4 Enzymes in Gynandropsis gynandra Mesophyll Cells

“…However, we extend this analysis to show that sequences within introns and interactions between 59 and 39 UTRs can also generate increased CA4 abundance. In maize, representing an independent C 4 lineage, introns direct increased expression of genes encoding NADP-dependent malic enzyme and aspartate aminotransferase (Nomura et al, 2005a(Nomura et al, , 2005b. Together, our data and these previous studies suggest that multiple alterations in cis to noncoding regions are a primary route through which the increased abundance of C 4 pathway enzymes evolved in multiple C 4 lineages.…”

“…For example, the increased abundance of C 4 enzymes can be conferred by elements within the promoter (Matsuoka et al, 1994;Gowik et al, 2004;Kajala et al, 2012;Wiludda et al, 2012), intron (Nomura et al, 2005b), or untranslated regions (UTRs) (Ali and Taylor, 2001;Wiludda et al, 2012). Similarly, cell specificity can be generated by the promoter (Matsuoka et al, 1994;Gowik et al, 2004), exon , or UTRs (Patel et al, 2004;Kajala et al, 2012).…”

Evolution and Function of acis-Regulatory Module for Mesophyll-Specific Gene Expression in the C4 DicotFlaveria trinervia

“…Even within the Poaceae, the expression of C 4 genes from the panicoid C 4 grasses Zea mays and Panicum miliaceum (Matsuoka et al, 1994;Nomura et al, 2005b) and the chloridoid C 4 grass Zoysia japonica (Nomura et al, 2005a) in the C 3 grass Oryza sativa did not generally result in the maintenance of cell specificity. While some C 4 gene promoters maintain their cell specificity of expression, others do not.…”

The Regulation of Gene Expression Required for C4Photosynthesis

“…When the rice 5 region was placed into maize, GUS accumulated in photosynthetic tissues and in both M and BS cells. In rice the 5 region to www.annualreviews.org • Gene Expression Required for C 4 Photosynthesis the gene encoding a cytosolic isoform of AspAT from Panicum miliaceum leads to light-inducible and preferential accumulation in M cells (92).…”

“…Our understanding of the extent to which proteins required in the BS of C 4 plants can be engineered into C 3 plants is based on studies of promoters of the genes encoding PEPCK, NADP-ME, AspAT, SSU, and the P subunit of glycine decarboxylase (GDCP) (24,80,91,92). Only the region 5 to the Zoysia japonica PCK gene encoding PEPCK (−1447 to +227, including the 5 UTR, first exon, first intron, and part of the second exon) linked to uidA generated accumulation of GUS in BS of rice (91).…”