Metabolism of soluble sugars in developing melon fruit: a global transcriptional view of the metabolic transition to sucrose accumulation.

The sweet melon fruit is characterized by a metabolic transition during its development that leads to extensive accumulation of the disaccharide sucrose in the mature fruit. While the biochemistry of the sugar metabolism pathway of the cucurbits has been well studied, a comprehensive analysis of the pathway at the transcriptional level allows for a global genomic view of sugar metabolism during fruit sink development. We identified 42 genes encoding the enzymatic reactions of the sugar metabolism pathway in melon. The expression pattern of the 42 genes during fruit development of the sweet melon cv Dulce was determined from a deep sequencing analysis performed by 454 pyrosequencing technology, comprising over 350,000 transcripts from four stages of developing melon fruit flesh, allowing for digital expression of the complete metabolic pathway. The results shed light on the transcriptional control of sugar metabolism in the developing sweet melon fruit, particularly the metabolic transition to sucrose accumulation, and point to a concerted metabolic transition that occurs during fruit development.

Improving plant stress tolerance and yield production: is the tonoplast aquaporin SlTIP2;2 a key to isohydric to anisohydric conversion?

Anisohydric plants are thought to be more drought tolerant than isohydric plants. However, the molecular mechanism determining whether the plant water potential during the day remains constant or not regardless of the evaporative demand (isohydric vs anisohydric plant) is not known. Here, it was hypothesized that aquaporins take part in this molecular mechanism determining the plant isohydric threshold. Using computational mining a key tonoplast aquaporin, tonoplast intrinsic protein 2;2 (SlTIP2;2), was selected within the large multifunctional gene family of tomato (Solanum lycopersicum) aquaporins based on its induction in response to abiotic stresses. SlTIP2;2-transformed plants (TOM-SlTIP2;2) were compared with controls in physiological assays at cellular and whole-plant levels. Constitutive expression of SlTIP2;2 increased the osmotic water permeability of the cell and whole-plant transpiration. Under drought, these plants transpired more and for longer periods than control plants, reaching a lower relative water content, a behavior characterizing anisohydric plants. In 3-yr consecutive commercial glasshouse trials, TOM-SlTIP2;2 showed significant increases in fruit yield, harvest index and plant mass relative to the control under both normal and water-stress conditions. In conclusion, it is proposed that the regulation mechanism controlling tonoplast water permeability might have a role in determining the whole-plant ishohydric threshold, and thus its abiotic stress tolerance.