A fruit-specific phospho enol pyruvate carboxylase is related to rapid growth of tomato fruit

Abstract

Malic and citric acids accumulate in cherry tomato (Lycopersicon esculentum Mill.) fruit during the period of rapid growth, from the end of cell division to the onset of ripening. The involvement of phospho enolpyruvate carboxylase (PEPCase, EC 4.1.1.31) in organic acid accumulation and tomato fruit development was investigated. Two PEPCases, named LYCes;Ppc1 and LYCes;Ppc2 and mapped to chromosomes 12 and 7, respectively, were shown to be differentially expressed during tomato fruit development. LYCes;Ppc1 mRNA was present in all fruit tissues and in all other plant organs examined. In contrast, LYCes;Ppc2 was strongly and specifically expressed in fruit from the end of cell division to ripening. No LYCes;Ppc2 expression was detected by northern blot in other plant tissues. In fruit, the increase in LYCes;Ppc2 mRNA was closely followed by an increase in fruit PEPCase protein and activity, and was coincident with the increased accumulation of malate and citrate during the initial period of rapid growth rate, from 8 to 20 days post anthesis. Localization of LYCes;Ppc2 mRNA in young tomato fruit by in situ hybridization revealed that LYCes;Ppc2 is preferentially expressed in large cells of the pericarp and in enlarging cells of the gel surrounding the seeds. Examination of the kinetic and regulatory properties of the PEPCases of growing and ripening fruit further showed that PEPCase in growing fruit is less sensitive to low pH and malate inhibition, indicating a high phosphorylation state and/or the presence of a PEPCase isoform with these characteristics. Taken together, these results indicate that in developing tomato fruit PEPCase is probably important in permitting the synthesis of organic acids to provide the turgor pressure necessary for cell expansion.

Changes in Transcriptional Profiles Are Associated with Early Fruit Tissue Specialization in Tomato

“…Many of these genes (up to 36% in the locular tissue) encode proteins with unknown functions or, alternatively, present no homology with known genes. Our findings correlate well for the few genes or enzymatic activities previously studied in the developing fruit (Laval-Martin et al, 1977;Schaffer and Petreikov, 1997;Rebers et al, 1999;RodriguezConception and Gruissem, 1999;Joubès et al, 2000;Lemaire-Chamley et al, 2000;Muir et al, 2001;Guillet et al, 2002;Busi et al, 2003;Obiadalla-ali et al, 2004). Interestingly, the repartition of the known genes into the different functional categories is very different between the exocarp and the locular tissue.…”

“…Several genes expressed in locular tissue (Table II) encode known proteins controlling the flux of water from the symplast and across the vacuolar membrane (the plasma membrane intrinsic protein [PIP] and TIP aquaporins; Maurel and Chrispeels, 2001;Ozga et al, 2002), the accumulation of soluble sugars in the vacuole (the vacuolar invertase that is controlled by the vacuolar processing enzyme VPEg, targeting to the vacuole, and the invertase inhibitor; Koch, 2004), and the accumulation of organic acids (citric and malic acids) used as counterions in the expanding vacuoles (the phosphoenolpyruvate carboxylase that controls a key step in organic acid synthesis and the zinc-finger homeodomain transcription factor, a putative regulator of its expression; Windhovel et al, 2001;Guillet et al, 2002). More complex roles may be fulfilled by TRAMP, a fruit-expressed PIP found in the locular tissue, since its inhibition by antisense technology altered the organic-acid-to-sugar ratio in the fruit (Chen et al, 2001).…”

Nuclear Magnetic Resonance Spectroscopy-Based Metabolite Profiling of Transgenic Tomato Fruit Engineered to Accumulate Spermidine and Spermine Reveals Enhanced Anabolic and Nitrogen-Carbon Interactions

“…PCR primers for tomato PEPC2 gene were designed (GenBank accession no. AJ313434; Guillet et al, 2002) and the amplicon included 144 bp of 3# untranslated region and a 39-bp coding sequence; the forward and reverse primers were 5#-atgaaaggtattgctgctgga-3# (LePEPC2RTF) and 5#-tcgagaagctactaaacaaagagg-3# (LePEPC2RTR), respectively. PCR primers for tomato NADP 1 -ICDH gene were designed (TIGR tomato gene index no.…”

Gene and Metabolite Regulatory Network Analysis of Early Developing Fruit Tissues Highlights New Candidate Genes for the Control of Tomato Fruit Composition and Development

“…Both the nutritional and the sensorial attributes are built throughout the successive phases of fruit development, namely cell division, cell expansion, and ripening. While the fruitripening process is obviously important (Giovannoni, 2001), there is also a growing body of evidence that supports the key role of early fruit development for the acquisition of several fruit quality traits, including the accumulation of sugars and organic acids (Guillet et al, 2002;Lemaire-Chamley et al, 2005;Petreikov et al, 2006), the determination of cell wall and texture characteristics (Chaïb et al, 2007), and the cuticle biosynthesis (Mintz-Oron et al, 2008). In the growing fruit, these processes mainly take place during the cell expansion phase, which sustains fruit growth by allowing a large increase in fruit cell volume linked with membrane and cell wall/synthesis and the con-comitant accumulation of water, mineral ions, and metabolites in the vacuoles, thereby conferring its fleshy characteristics to the fruit.…”