Molecular regulation of sucrose catabolism and sugar transport for development, defence and phloem function

Abstract

Sucrose (Suc) is the major end product of photosynthesis in mesophyll cells of most vascular plants. It is loaded into phloem of mature leaves for long-distance translocation to non-photosynthetic organs where it is unloaded for diverse uses. Clearly, Suc transport and metabolism is central to plant growth and development and the functionality of the entire vascular system. Despite vast information in the literature about the physiological roles of individual sugar metabolic enzymes and transporters, there is a lack of systematic evaluation about their molecular regulation from transcriptional to post-translational levels. Knowledge on this topic is essential for understanding and improving plant development, optimizing resource distribution and increasing crop productivity. We therefore focused our analyses on molecular control of key players in Suc metabolism and transport, including: (i) the identification of promoter elements responsive to sugars and hormones or targeted by transcription factors and microRNAs degrading transcripts of target genes; and (ii) modulation of enzyme and transporter activities through protein-protein interactions and other post-translational modifications. We have highlighted major remaining questions and discussed opportunities to exploit current understanding to gain new insights into molecular control of carbon partitioning for improving plant performance.

Preliminary Variations in Physiological Modules When <i>sub</i>1<i>A</i> QTL Is under Soil-Moisture Deficit Stress

“…In earlier reports, sub1A is characterized in a stable manner for regulation of the protein metabolism [26]. Carbohydrate metabolism appears to be more striking features in present experiment.…”

OsINV3 and Its Homolog, OsINV2, Control Grain Size in Rice

“…Vacuolar invertases have been proposed to regulate cell expansion, osmotic pressure, sugar signals, sucrose accumulation, and sucrose concentration, especially during the expansion phases of sink organs [32]. In rice, two VIN isogenes, OsINV2 and OsINV3, have been identified.…”

“…Grain biomass accumulation is dependent on sucrose supply and hexose assimilation along the transport pathway from leaf to developing caryopsis [25,27,28,32]. Sugar transporters play pivotal roles in carbon partitioning by mediating long distance sucrose transport from source leaves to sink [25].…”

Regulatory roles of sugars in plant growth and development

“…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.…”