Isolation and characterization of cDNA clones for NADP-malic enzyme from leaves ofFlaveria: transcript abundance distinguishes C3, C3?C4 and C4 photosynthetic types

Abstract

To study the control of enhanced synthesis of enzymes associated with C4 photosynthesis relative to non-C4 plants, we investigated the expression of NADP-malic enzyme (NADP-ME) in different photosynthetic types of Flaveria. Complementary DNA clones encoding NADP-ME were constructed using poly(A)+ RNA from leaves of Flaveria trinervia (C4) and F. linearis (C3-C4) and identified by homology to a cDNA clone (500 bp) encoding NADP-ME from maize (Zea mays L. [39]). The sequence of one clone from each species was determined. The Flaveria clones were 90% homologous over a 564 nucleotide region encoding the carboxy terminal end of the derived polypeptide; sequence similarity to the maize transcript in this region was 71%. Both Flaveria clones detected a 2/3 kb transcript by hybridization to poly(A)+ RNA from expanding leaves of F. trinervia, F. linearis and F. pringlei (C3). The level of transcripts paralleled previously observed NADP-ME activity and abundance differences determined in these species, suggesting that control of the expression of NADP-ME in different photosynthetic types is predominantly at the transcriptional/post-transcriptional level. Southern analysis of genomic DNAs from F. trinervia, F. linearis and F. pringlei indicated a low copy number for this gene in all three species.

Two Genes Encode Highly Similar Chloroplastic NADP-Malic Enzymes in Flaveria (Implications for the Evolution of C4 Photosynthesis)

“…This cDNA, termed hmell, was identified using a maize NADP-ME cDNA (Rothermel and Nelson, 1989) as probe. The nucleotide sequence of Ame11 was >99% identical with that of the middle region of two NADP-ME cDNAs previously reported to encode the C, form of the enzyme in the closely related species F. trinervia (data not shown; Borsch and Westhoff, 1990;Rajeevan et al, 1991).…”

“…3C). Furthermore, comparison of the 3' UTR of the reported partia1 NADP-ME cDNA from the C,-C, intermediate species F. linearis (Rajeevan et al, 1991) with those of Mel and Me2 indicated that the F. linearis cDNA, like the F. pringlei cDNA, was much more similar to Me2 than to Mel (data not shown).…”

“…Full-length cDNA clones encoding NADP-ME have been reported from the C, species Flaveria trinervia (Borsch and Westhoff, 1990) and the C, species Flaveria pringlei (Lipka et al, 1994). In addition, a partial cDNA clone has been reported from the C,-C, intermediate species Flaveria linearis (Rajeevan et al, 1991). Based on Southern blot analysis using partial NADP-ME cDNAs from F. linearis and F. trinervia to probe genomic DNA from these two species and from F. pringlei, Rajeevan et al (1991) concluded that NADP-ME is encoded by a small gene family, possibly consisting of three members.…”

“…In addition, a partial cDNA clone has been reported from the C,-C, intermediate species Flaveria linearis (Rajeevan et al, 1991). Based on Southern blot analysis using partial NADP-ME cDNAs from F. linearis and F. trinervia to probe genomic DNA from these two species and from F. pringlei, Rajeevan et al (1991) concluded that NADP-ME is encoded by a small gene family, possibly consisting of three members. The nature of these genes and the number that are involved in C, photosynthesis were not determined.…”

“…Vol. 111, 1996 of the F. trinervia or F. pringlei cDNAs (Borsch and Westhoff, 1990;Rajeevan et al, 1991;Lipka et al, 1994). In these latter studies, the high degree of similarity of the NADP-ME-coding regions would have allowed the determination of the total amount of NADP-ME mRNA present; however, the probes used would not have discriminated between mRNA derived from Mel-or Me2-type NADP-ME genes.…”