Phosphorus (P), an element required for plant growth, fruit set, fruit development, and fruit ripening, can be deficient or unavailable in agricultural soils. Previously, it was shown that over-expression of a proton-pyrophosphatase gene AVP1/AVP1D (AVP1DOX) in Arabidopsis, rice, and tomato resulted in the enhancement of root branching and overall mass with the result of increased mineral P acquisition. However, although AVP1 over-expression also increased shoot biomass in Arabidopsis, this effect was not observed in tomato under phosphate-sufficient conditions. AVP1DOX tomato plants exhibited increased rootward auxin transport and root acidification compared with control plants. AVP1DOX tomato plants were analysed in detail under limiting P conditions in greenhouse and field trials. AVP1DOX plants produced 25% (P=0.001) more marketable ripened fruit per plant under P-deficient conditions compared with the controls. Further, under low phosphate conditions, AVP1DOX plants displayed increased phosphate transport from leaf (source) to fruit (sink) compared to controls. AVP1DOX plants also showed an 11% increase in transplant survival (P<0.01) in both greenhouse and field trials compared with the control plants. These results suggest that selection of tomato cultivars for increased proton pyrophosphatase gene expression could be useful when selecting for cultivars to be grown on marginal soils.

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Anthocyanins are important pigments in peach fruit and are beneficial to human health. Sugars are both energy-storing and signaling molecules and their roles in inducing anthocyanin biosynthesis have received a great deal of research attention. However, the mechanism by which sugars induce anthocyanin biosynthesis in peach fruit is unknown. In order to understand this induction mechanism, comprehensive transcriptome and metabolome were performed in fruit flesh treated with four different sugars for 12 and 24 h, respectively. Here, we found that cyanidin-3-O-(6-O-p-coumaroyl) glucosides accumulated in fruit flesh treated with glucose, sucrose, sorbitol, and fructose in vitro. Two key structural genes of the anthocyanin biosynthesis pathway, namely, PpDFR and PpUFGT, were upregulated in the flesh of sugar-treated peach fruit. By contrast, the two main transcription factors (TFs) PpMYB10.1 and PpBL regulating anthocyanin biosynthetic genes in peach fruit were not upregulated accordingly. Interestingly, two MYB family genes (PpMYB6 and PpMYB44-like) and three bHLH family genes (PpbHLH35, PpbHLH51, and PpbHLH36-like) were upregulated. A dual luciferase assay revealed that PpMYB6 strongly activated the PpUFGT promoter when it was co-infiltrated with PpbHLH35, PpbHLH51, and PpbHLH36-like. When PpMYB44-like was co-infiltrated with PpbHLH35, it also potently activated the PpUFGT promoter. The results of this study help clarify the molecular mechanisms by which glucose, sucrose, sorbitol, and fructose regulate anthocyanin accumulation in peach fruit.