Metabolite transport and associated sugar signalling systems underpinning source/sink interactions

Abstract

Metabolite transport between organelles, cells and source and sink tissues not only enables pathway co-ordination but it also facilitates whole plant communication, particularly in the transmission of information concerning resource availability. Carbon assimilation is co-ordinated with nitrogen assimilation to ensure that the building blocks of biomass production, amino acids and carbon skeletons, are available at the required amounts and stoichiometry, with associated transport processes making certain that these essential resources are transported from their sites of synthesis to those of utilisation. Of the many possible posttranslational mechanisms that might participate in efficient co-ordination of metabolism and transport only reversible thiol-disulphide exchange mechanisms have been described in detail. Sucrose and trehalose metabolism are intertwined in the signalling hub that ensures appropriate resource allocation to drive growth and development under optimal and stress conditions, with trehalose-6-phosphate acting as an important signal for sucrose availability. The formidable suite of plant metabolite transporters provides enormous flexibility and adaptability in inter-pathway coordination and source-sink interactions. Focussing on the carbon metabolism network, we highlight the functions of different transporter families, and the important of thioredoxins in the metabolic dialogue between source and sink tissues. In addition, we address how these systems can be tailored for crop improvement.

Plant Desiccation Tolerance and its Regulation in the Foliage of Resurrection “Flowering-Plant” Species

“…T6P-inhibited SnRK1 will up-regulate carbohydrate storage, prime gene expression for growth, growth recovery and signals satiety, whereas uninhibited SnRK1 will signal starvation, catabolism and will slow growth. Indeed, the T6P:SnRK1 relationship is considered a major player in directing carbohydrates between source and sink tissues, and can be a key factor in the survival of environmental stress [116][117][118][119]. This has been addressed in Arabidopsis, where accumulated T6P under sink-limited stress conditions inhibits SnRK1 activity, and thus allows synthesis and growth to resume rapidly once the growth limiting stress conditions were alleviated [118].…”

Regulatory roles of sugars in plant growth and development

“…Much research has been recently devoted to deciphering the mechanisms of growth, developmental regulation, and interactions between different signaling pathways in plant cells [1][2][3][4][5][6][7][8]. One of the most interesting aspects has been the demonstration of the regulatory function of sugars -molecules known for a long time to be involved in basal cell metabolism, and which are substrates or products of numerous chemical reactions.…”

“…Sugars affect the growth, development, and metabolism of leaves, shoots, roots, and other plant organs [2,3,5,6,30,36,37]. In leaves, changes in glucose or sucrose levels mainly affect photosynthesis intensity and export of assimilates (high sugar levels often decrease photosynthesis rate), whereas changes in transport and sugar concentrations in roots mainly affect respiratory metabolism and storage [9,28,29].…”

“…The following strategies were used in order to select the appropriate mutants: (i) if high sugar concentrations in the medium inhibited germination and seedling development, then the seedlings showing development were nonsusceptible to sugars (for example, gin -glucose insensitive, rsr -reduced sugar response, sis -sucrose insensitive, or migmannose insensitive germination); (ii) seeds incapable of germinating (and growing) on media containing sugar concentrations that did not inhibit the development of other plants were mutants that were excessively sensitive to sugars (for example, gss -glucose super sensitive, sss -sucrose super sensitive, or hsr -high sugar-response). During the last decades, a huge progress has been made in understanding the physiological roles of sugar-metabolizing enzymes or sugar transporters, mainly by using transgenic/ mutational approaches [2,9,18,55,56,75,76]. The use of novel mutants (and transgenic plants) that specifically react to different sugars, as well as hormonal mutants, will certainly be helpful in subsequent studies on the regulatory role of sugars throughout plant development and in the elucidation of crosstalk with other signaling pathways.…”

Transitioning to the Next Phase: The Role of Sugar Signaling throughout the Plant Life Cycle

“…It accumulates under conditions when Suc content is high and has been proposed to act as a signal for Suc availability (Nunes et al, 2013a;Yadav et al, 2014;Figueroa and Lunn, 2016). The role of T6P in regulating sourcesink interactions during plant development is further discussed by O'Hara et al (2013) and Griffiths et al (2016a).…”