Oil palm can accumulate up to 90% oil in its mesocarp, the highest level observed in the plant kingdom. In contrast, the closely related date palm accumulates almost exclusively sugars. To gain insight into the mechanisms that lead to such an extreme difference in carbon partitioning, the transcriptome and metabolite content of oil palm and date palm were compared during mesocarp development. Compared with date palm, the high oil content in oil palm was associated with much higher transcript levels for all fatty acid synthesis enzymes, specific plastid transporters, and key enzymes of plastidial carbon metabolism, including phosphofructokinase, pyruvate kinase, and pyruvate dehydrogenase. Transcripts representing an ortholog of the WRI1 transcription factor were 57-fold higher in oil palm relative to date palm and displayed a temporal pattern similar to its target genes. Unexpectedly, despite more than a 100-fold difference in flux to lipids, most enzymes of triacylglycerol assembly were expressed at similar levels in oil palm and date palm. Similarly, transcript levels for all but one cytosolic enzyme of glycolysis were comparable in both species. Together, these data point to synthesis of fatty acids and supply of pyruvate in the plastid, rather than acyl assembly into triacylglycerol, as a major control over the storage of oil in the mesocarp of oil palm. In addition to greatly increasing molecular resources devoted to oil palm and date palm, the combination of temporal and comparative studies illustrates how deep sequencing can provide insights into gene expression patterns of two species that lack genome sequence information.

Magnesium deficiency has been reported to affect plant growth and biomass partitioning between root and shoot. The present work aims to identify how Mg deficiency alters carbon partitioning in sugar beet (Beta vulgaris L.) plants. Fresh biomass, Mg and sugar contents were followed in diverse organs over 20 days under Mg-sufficient and Mg-deficient conditions. At the end of the treatment, the aerial biomass, but not the root biomass, of Mg-deficient plants was lower compared to control plants. A clear inverse relationship between Mg and sugar contents in leaves was found. Mg deficiency promoted a marked increase in sucrose and starch accumulation in the uppermost expanded leaves, which also had the lowest content of Mg among all the leaves of the rosette. The oldest leaves maintained a higher Mg content. [14C]Sucrose labelling showed that sucrose export from the uppermost expanded leaves was inhibited. In contrast, sucrose export from the oldest leaves, which are close to, and export mainly to, the roots, was not restricted. In response to Mg deficiency, the BvSUT1 gene encoding a companion cell sucrose/H+ symporter was induced in the uppermost expanded leaves, but without further enhancement of sucrose loading into the phloem. The observed increase in BvSUT1 gene expression supports the idea that sucrose loading into the phloem is defective, resulting in its accumulation in the leaf.

All flowering plants produce S-methylmethionine (SMM) from Met and have a separate mechanism to convert SMM back to Met. The functions of SMM and the reasons for its interconversion with Met are not known. In this study, by using the aphid stylet collection method together with mass spectral and radiolabeling analyses, we established that l-SMM is a major constituent of the phloem sap moving to wheat ears. The SMM level in the phloem ( approximately 2% of free amino acids) was 1.5-fold that of glutathione, indicating that SMM could contribute approximately half the sulfur needed for grain protein synthesis. Similarly, l-SMM was a prominently labeled product in phloem exudates obtained by EDTA treatment of detached leaves from plants of the Poaceae, Fabaceae, Asteraceae, Brassicaceae, and Cucurbitaceae that were given l-(35)S-Met. cDNA clones for the enzyme that catalyzes SMM synthesis (S-adenosylMet:Met S-methyltransferase; EC 2.1.1.12) were isolated from Wollastonia biflora, maize, and Arabidopsis. The deduced amino acid sequences revealed the expected methyltransferase domain ( approximately 300 residues at the N terminus), plus an 800-residue C-terminal region sharing significant similarity with aminotransferases and other pyridoxal 5'-phosphate-dependent enzymes. These results indicate that SMM has a previously unrecognized but often major role in sulfur transport in flowering plants and that evolution of SMM synthesis in this group involved a gene fusion event. The resulting bipartite enzyme is unlike any other known methyltransferase.

The sequence encompassing the cai genes of Escherichia coli, which encode the carnitine pathway, has been determined. Apart from the already identified caiB gene coding for the carnitine dehydratase, five additional open reading frames were identified. They belong to the caiTABCDE operon, which was shown to be located at the first minute on the chromosome and transcribed during anaerobic growth in the presence of carnitine. The activity of carnitine dehydratase was dependent on the CRP regulatory protein and strongly enhanced in the absence of a functional H-NS protein, in relation to the consensus sequences detected in the promoter region of the cai operon. In vivo expression studies led to the synthesis of five polypeptides in addition to CaiB, with predicted molecular masses of 56,613 Da (CaiT), 42,564 Da (CaiA), 59,311 Da (CaiC), 32,329 Da (CaiD) and 21,930 Da (CaiE). Amino acid sequence similarity or enzymatic analysis supported the function assigned to each protein. CaiT was suggested to be the transport system for carnitine or betaines, CaiA an oxidoreduction enzyme, and CaiC a crotonobetaine/carnitine CoA ligase. CaiD bears strong homology with enoyl hydratases/isomerases. Overproduction of CaiE was shown to stimulate the carnitine racemase activity of the CaiD protein and to markedly increase the basal level of carnitine dehydratase activity. It is inferred that CaiE is an enzyme involved in the synthesis or the activation of the still unknown cofactor required for carnitine dehydratase and carnitine racemase activities. Taken together, these data suggest that the carnitine pathway in E. coli resembles that found in a strain situated between Agrobacterium and Rhizobium.

All flowering plants produce S -methylmethionine (SMM) from Met and have a separate mechanism to convert SMM back to Met. The functions of SMM and the reasons for its interconversion with Met are not known. In this study, by using the aphid stylet collection method together with mass spectral and radiolabeling analyses, we established that L -SMM is a major constituent of the phloem sap moving to wheat ears. The SMM level in the phloem ( ‫ف‬ 2% of free amino acids) was 1.5-fold that of glutathione, indicating that SMM could contribute approximately half the sulfur needed for grain protein synthesis. Similarly, L -SMM was a prominently labeled product in phloem exudates obtained by EDTA treatment of detached leaves from plants of the Poaceae, Fabaceae, Asteraceae, Brassicaceae, and Cucurbitaceae that were given L -35 S-Met. cDNA clones for the enzyme that catalyzes SMM synthesis ( S -adenosylMet:Met S -methyltransferase; EC 2.1.1.12) were isolated from Wollastonia biflora , maize, and Arabidopsis. The deduced amino acid sequences revealed the expected methyltransferase domain ( ‫ف‬ 300 residues at the N terminus), plus an 800-residue C-terminal region sharing significant similarity with aminotransferases and other pyridoxal 5 -phosphate-dependent enzymes. These results indicate that SMM has a previously unrecognized but often major role in sulfur transport in flowering plants and that evolution of SMM synthesis in this group involved a gene fusion event. The resulting bipartite enzyme is unlike any other known methyltransferase. INTRODUCTIONPlant Met metabolism differs from that in other organisms by involving S -methylmethionine (SMM). SMM is a ubiquitous constituent of the free amino acid pool in flowering plants, occurring in leaves, roots, and other organs at levels that typically range from 0.5 to 3 mol g Ϫ 1 dry weight, a concentration that is often higher than those of Met or S -adenosylmethionine (AdoMet) (Giovanelli et al., 1980;Mudd and Datko, 1990;Bezzubov and Gessler, 1992). SMM also has been detected as a metabolite of radiolabeled L -Met in all flowering plants tested ( Ͼ 50 species from Ͼ 20 families; Paquet et al., 1995). As shown in Figure 1, SMM is formed from L -Met via the action of AdoMet:Met S -methyltransferase (MMT; EC 2.1.1.12) and can be reconverted to Met by donating a methyl group to L -homocysteine (Hcy) in a reaction catalyzed by Hcy S -methyltransferase (HMT; EC 2.1.1.10; Giovanelli et al., 1980;Mudd and Datko, 1990). The tandem action of MMT and HMT, together with S -adenosyl-L -Hcy hydrolase, constitutes the SMM cycle, which is apparently futile (Mudd and Datko, 1990).As expected from the universality of SMM, MMT activity has been found in many flowering plants (Giovanelli et al., 1980;Mudd and Datko, 1990). It has been purified from leaves of Wollastonia biflora (James et al., 1995a) and from germinating barley (Pimenta et al., 1998), and it is known to have subunits of ‫ف‬ 115 kD. Because this is approximately three times larger than any other small-molecule methyltransferase (F...

Plants synthesize S-methylmethionine (SMM) from Sadenosylmethionine (AdoMet), and methionine (Met) by a unique reaction and, like other organisms, use SMM as a methyl donor for Met synthesis from homocysteine (Hcy). These reactions comprise the SMM cycle. Two Arabidopsis cDNAs specifying enzymes that mediate the SMM 3 Met reaction (SMM:Hcy S-methyltransferase, HMT) were identified by homology and authenticated by complementing an Escherichia coli yagD mutant and by detecting HMT activity in complemented cells. Gel blot analyses indicate that these enzymes, AtHMT-1 and -2, are encoded by single copy genes. The deduced polypeptides are similar in size (36 kDa), share a zincbinding motif, lack obvious targeting sequences, and are 55% identical to each other. The recombinant enzymes exist as monomers. AtHMT-1 and -2 both utilize L-SMM or (S,S)-AdoMet as a methyl donor in vitro and have higher affinities for SMM. Both enzymes also use either methyl donor in vivo because both restore the ability to utilize AdoMet or SMM to a yeast HMT mutant. However, AtHMT-1 is strongly inhibited by Met, whereas AtHMT-2 is not, a difference that could be crucial to the control of flux through the HMT reaction and the SMM cycle. Plant HMT is known to transfer the pro-R methyl group of SMM. This enabled us to use recombinant AtHMT-1 to establish that the other enzyme of the SMM cycle, AdoMet:Met S-methyltransferase, introduces the pro-S methyl group. These opposing stereoselectivities suggest a way to measure in vivo flux through the SMM cycle.

The oil palm fruit mesocarp contains high lipase activity that increases free fatty acids and necessitates post-harvest inactivation by heat treatment of fruit bunches. Even before heat treatment the mesocarp lipase activity causes consequential oil losses and requires costly measures to limit free fatty acids quantities. Here we demonstrate that elite low-lipase lines yield oil with substantially less free fatty acids than standard genotypes, allowing more flexibility for post-harvest fruit processing and extended ripening for increased yields. We identify the lipase and its gene cosegregates with the low-/high-lipase trait, providing breeders a marker to rapidly identify potent elite genitors and introgress the trait into major cultivars. Overall, economic gains brought by wide adoption of this material could represent up to one billion dollars per year. Expected benefits concern all planters but are likely to be highest for African smallholders who would be more able to produce oil that meets international quality standards.

Anaerobic carnitine metabolism in Escherichia coli was recently shown to involve six genes organized in the cai operon and located at the first minute on the chromosome. The DNA sequence lying at the 5' end of the cai locus was further investigated. It contains four open reading frames organized as an operon. In vivo overexpression of this DNA region revealed four polypeptides with apparent molecular masses of 27, 33, 45 and 6 kDa. These proteins displayed significant amino acid sequence homologies with polypeptides encoded by the fixABCX operons from Azorhizobium caulinodans and Rhizobium meliloti. The four ORFs were thus named fixABCX. The first two gene products were also found to share a high degree of sequence similarity with the subunits beta and alpha, respectively, of mammalian electron transfer flavoproteins, suggesting a role for these proteins in a redox reaction. A singly polycistronic 5 kb mRNA transcript was detected in Northern blots under anaerobic conditions in the presence of DL-carnitine. Expression of a fixA-lacZ transcriptional fusion was induced by L(-)-carnitine and crotonobetaine but not by D(+)-carnitine, gamma-butyrobetaine, glycinebetaine and choline as found previously for the carnitine pathway. Similarly, the fix operon was repressed by glucose and nitrate. Moreover, expression of the fix operon was induced by the global regulatory proteins CRP and FNR and repressed by the histone-like protein H-NS. All these regulatory proteins have been shown also to control expression of carnitine enzymes. Results from Northern blots and lacZ fusion studies indicate a common regulation of expression of fix and cai operons, which implies a physiological linkage between these two loci.