Cloning and expression analysis of vacuolar H+-ATPase 69-kDa catalytic subunit cDNA in citrus (Citrus unshiu marc.)1

Fruit-specific V-ATPase suppression in antisense-transgenic tomato reduces fruit growth and seed formation

The vacuole is a large, multifunctional organelle related to the processes of cell expansion, solute accumulation, regulation of cytoplasmic ion concentrations, pH homeostasis and osmoregulation, which are directly or indirectly achieved by vacuolar H+-pumps: vacuolar H+-ATPase (V-ATPase; EC 3.6.1.3) and vacuolar H+-pyrophosphatase (V-PPase; EC 3.6.1.1). In this study, we produced antisense-transgenic tomatoes (Lycopersicon esculentum L.) of the V-ATPase A subunit, which is under the control of the fruit-specific 2A11 promoter. One beta-glucuronidase (GUS)-transgenic line (GUS control) and seven A subunit antisense-transgenic lines were obtained. The amount of V-ATPase A subunit mRNA in fruit decreased in all antisense-transgenic lines, but in leaves showed no difference compared with the GUS control line and the nontransformant, suggesting that suppression of the V-ATPase A subunit by a 2A11 promoter is limited to fruit. The antisense-transgenic plants had smaller fruits compared with the GUS control line and the nontransformant. Surprisingly, fruits from the antisense-transgenic plants, except the fruit that still had relatively high expression of A subunit mRNA, had few seeds. Sucrose concentration in fruits from the antisense-transgenic plants increased, but glucose and fructose concentrations did not change. These results show the importance of V-ATPase, not only in fruit growth, but also in seed formation and in sugar composition of tomato fruit.

Isolation and characterization of six peach cDNAs encoding key proteins in organic acid metabolism and solute accumulation: involvement in regulating peach fruit acidity

As in many other fleshy fruits, the predominant organic acids in ripe peach (Prunus persica (L.) Batsch) fruit are malic and citric acids. The accumulation of these metabolites in fruit flesh is regulated during fruit development. Six peach fruit-related genes implicated in organic acid metabolism (mitochondrial citrate synthase; cytosolic NAD-dependent malate dehydrogenase, and cytosolic NADP-dependent isocitrate dehydrogenase) and storage (vacuolar proton translocating pumps: one vacuolar H+-ATPase, and two vacuolar H+-pyrophosphatases) were cloned. Five of these peach genes were homologous to genes isolated from fruit in other fleshy fruit species. Phylogenetic and expression analyses suggested the existence of a particular vacuolar pyrophosphatase highly expressed in fruit. The sixth gene was the first cytosolic NAD-dependent malate dehydrogenase gene isolated from fruit. Gene expression was studied during the fruit development of two peach cultivars, a normal-acid (Fantasia) and a low-acid (Jalousia) cultivar. The overall expression patterns of the organic acid-related genes appeared strikingly similar for the two cultivars. The genes involved in organic acid metabolism showed a stronger expression in ripening fruit than during the earlier phases of development, but their expression patterns were not necessarily correlated with the changes in organic acid contents. The tonoplast proton pumps showed a biphasic expression pattern more consistent with the patterns of organic acid accumulation, and the tonoplast pyrophosphatases were more highly expressed in the fruit of the low-acid cultivar during the second rapid growth phase of the fruit.