NADP-malic enzyme ([E.G. 1.1.1.40]: ME) is a key enzyme involved in the fixation of carbon dioxide in the C4 photosynthesis. We isolated a cDNA fragment (0.5 kbp; the middle portion in the coding region) for an ME by RT-PCR based upon nucleotide sequences in the conserved regions of the cDNAs previously reported (Edwards and Andreo 1992). The nucleotide sequence was consistent with the sequence of a rice ME cDNA reported by Fushimi et al. (1994). RFLP mapping was carried out using an F₂ population derived from the cross, 'Kasalath' (indica) x 'FL134' (japonica). The method has been described previously (Saito et al. 1991). Based on Southern analysis with this fragment as probe, we detected the single band which shows an RFLP between the BamHI-digested total DNAs from the parental lines. The locus of this ME cDNA (XcrMal1; an RFLP locus of the cDNA clone for rice C4 ME) was located between two RFLP loci, 4.8 ± 1.6cM from XgrPepc (Phosphoeno/pyruvate carboxylase [=PEPCase] gene) and 1.1 ± 0.8cM from XNbp359, previously mapped on the chromosome 1 (Saito et al. 1991). Causse et al. (1994) has localized a locus of a rice ME (Mall, using isozyme analylsis) on the chromosome 1 of their map. The relationship between the map by Saito et al. ( 1991 ) and that by Causse et al.(1994) has been determined (Xiao et al. 1992). We concluded that the locus for this ME cDNA probably coincided with the Mal1 locus by Causse et al. (1994).

Both C4 ME and C4 PEPCase act important roles in C4 photosynthesis. Although rice is known as a C3 plant, it has been suggested that C4 type photosynthesis takes place in the lemma and palea (Imaizumi et al. 1990). The locus of XgrPepc has been determined using a fragment included in the genomic clone as the probe (Saito et al. 1991), which is the rice counterpart of the maize C4 PEPCase (Imaizurni and Matsuoka, pers. com.). The fact that close linkage in rice genome was found between these two genes involved in the carbon fixation pathway seems to be an evolutionary interesting event. This linkage relation was compared with those in the linkage maps of wheat and maize. As shown in Table 1, in the wheat and maize genomes, both loci for a ME and a C4 PEPCase were found on the separate chromosomes, while the close linkage between both loci was only found in the rice genome. As judged from these data for other orthological loci, it appears that chromosomal rearrangement occurred in the rice genome between two separate chromosomes carrying each of the genes for the ME (XcrMal1) and C4 PEPCase (XgrPepc) after speciation of primitive rice from the ancestral Gramineae species. In addition, it has been reported that, in this region of rice chromosome 1, there is a disruption

Research Notes 105

Data on this table are cited from Ahn et all. (1993) mainly, and from this study^a, Causse et al. (1992)^b. Saito et al. (1991)^c,Chao et al. (1989)^d and O'Brien (1993: from chapters by Burr etal, and Coe and Neuffer)^c. X indicates basic prefix for DNA markers.

of synteny to the syntenous wheat chromosome, that is, wheat chromosome 3 (Ahn et al. 1993: Kurata et al. 1994), possibly due to chromosomal rearrangement in the rice genome.

Chao, S., P.J. Sharp, A.J. Worland, E.J. Warham, R.M.D. Koebner and M.D. Gale, 1989. RFLP-based genetic

Edwards, G.E.and C.S. Andreo. 1992. NADP-malic enzyme from plants. Phytochemistry 31: 1845-1857.

Fushimi, T., M. Umeda, T Shimazaki, A. Kato, K. Toriyama and H. Uchimiya, 1994. Nucleotide sequence of a

rice cDNA similar to a maize NADP-dependent malic enzyme. Plant Mol. Biol. 24: 965-967.

Kurata, N.,G. Moore, Y. Nagamura, T. Foote, M. Yano, Y. Minobe and M. Gale, 1994. Conservation of

genome structure between rice and wheat. Bio/Technology 12: 276-278.

O'Brien, S.J., 1993. Genetic Map: Locus Maps of Complex Genoines. 6th edn. Book 6 Plants. Cold Spring

106 Rice Genetics Newsletter Vol. 14

Xiao, J., T. Fulton,. S. McCouch, S. Tanksley, N. Kishimoto, R. Ohsawa, Y. Ukai and A. Saito, 1992.

Progress in integration of the molecular maps in rice. RGN 9: 124-128.