Fruit Salad in the Lab: Comparing Botanical Species to Help Deciphering Fruit Primary Metabolism

Abstract

Although fleshy fruit species are economically important worldwide and crucial for human nutrition, the regulation of their fruit metabolism remains to be described finely. Fruit species differ in the origin of the tissue constituting the flesh, duration of fruit development, coordination of ripening changes (climacteric vs. non-climacteric type) and biochemical composition at ripeness is linked to sweetness and acidity. The main constituents of mature fruit result from different strategies of carbon transport and metabolism. Thus, the timing and nature of phloem loading and unloading can largely differ from one species to another. Furthermore, accumulations and transformations of major soluble sugars, organic acids, amino acids, starch and cell walls are very variable among fruit species. Comparing fruit species therefore appears as a valuable way to get a better understanding of metabolism. On the one hand, the comparison of results of studies about species of different botanical families allows pointing the drivers of sugar or organic acid accumulation but this kind of comparison is often hampered by heterogeneous analysis approaches applied in each study and incomplete dataset. On the other hand, cross-species studies remain rare but have brought new insights into key aspects of primary metabolism regulation. In addition, new tools for multi-species comparisons are currently emerging, including meta-analyses or re-use of shared metabolic or genomic data, and comparative metabolic flux or process-based modeling. All these approaches contribute to the identification of the metabolic factors that influence fruit growth and quality, in order to adjust their levels with breeding or cultural practices, with respect to improving fruit traits.

Metabolomics to Exploit the Primed Immune System of Tomato Fruit

“…The binding of BABA by an aspartyl-tRNA synthetase blocks the enzyme, consequently triggering the accumulation of its canonical substrate, uncharged tRNA, which leads to changes in amino acid pools in the plant, therefore affecting primary metabolism [20]. Subsequent signalling modulations might result from an alteration in amino acid precursors (e.g., ethylene, auxin) that would alter fruit production [37].…”

Get the Balance Right: ROS Homeostasis and Redox Signalling in Fruit

“…The redox hub consists of all the molecular partners able to generate, process or trigger oxidative signals, whilst the resulting redox signalling can modulate the physiology of plant organs including fruits (Mittler, 2017; Noctor et al, 2018). Fruits are a major source of central metabolites (Osorio et al, 2013a; Roch et al, 2019), such as carbohydrates, lipids, amino and organic acids, but also vitamins and other antioxidant metabolites that play important roles in fruit biology ( Figure 3 ). Besides, redox status is also at the heart of the control of metabolic processes (Geigenberger and Fernie, 2014).…”

“…They constitute a remarkable source of food worldwide and contain a plethora of natural compounds with various benefits for human health and nutrition, including vitamins, nutrients, fibres, proteins and minerals (Baldet et al, 2014; Rodriguez-Casado, 2016; Padayachee et al, 2017). Despite having high concentrations in carbohydrates, fruits usually exhibit reduced photosynthetic activity, but sometimes high respiration rates, in particular for climacteric fruits, such as tomato (Roch et al, 2019). As for other vegetative plant tissues, fruit biology involves redox reactions and generates ROS.…”

Sugar Metabolism in Stone Fruit: Source-Sink Relationships and Environmental and Agronomical Effects

“…Sugar transport, direction, and volume are determined by sink position and relative sink strength. Carbohydrates produced in leaf mesophyll are loaded into the phloem systems and unloaded in energy-demanding or storage tissues (sinks); both the mechanisms can be apoplastic (sugars cross the cell membrane) or symplastic (exclusively through the plasmodesmata-connected cells; De Schepper et al, 2013;Roch et al, 2019). Among the sugars synthesized in plants, only a small number of them, generally highly soluble and chemically inert, are transported in the phloem over a long-distance.…”

“…The available data suggest that phloem loading can occur through an apoplastic or a symplastic path or possibly a combination of both, depending on the species and the sugar considered (Flora and Madore, 1993;Noiraud et al, 2001;Nadwodnik and Lohaus, 2008; Figure 1). The passive symplasmic mechanism has been identified in most fruit trees of Rosaceae family (Reidel et al, 2009;Fu et al, 2011;Roch et al, 2019). Despite the importance of sorbitol in this family, sorbitol transporters were found only in sink organs (Gao et al, 2003;Watari et al, 2004), making the knowledge on polyol phloem loading extremely limited.…”