The Differential Expression of Sucrose Synthase in Relation to Diverse Patterns of Carbon Partitioning in Developing Cotton Seed

Abstract

Developing cotton (Gossypium hirsutum L.) seed exhibits complex patterns of carbon allocation in which incoming sucrose (Suc) is partitioned to three major sinks: the fibers, seed coat, and cotyledons, which synthesize cellulose, starch, and storage proteins or oils, respectively. In this study we investigated the role of Suc synthase (SuSy) in the mobilization of Suc into such sinks. Assessments of SuSy gene expression at various levels led to the surprising conclusion that, in contrast to that found for other plants, SuSy does not appear to play a role in starch synthesis in the cotton seed. However, our demonstration of functional symplastic connections between the phloem-unloading area and the fiber cells, as well as the SuSy expression pattern in fibers, indicates a major role of SuSy in partitioning carbon to fiber cellulose synthesis. SuSy expression is also high in transfer cells of the seed coat facing the cotyledons. Such high levels of SuSy could contribute to the synthesis of the thickened cell walls and to the energy generation for Suc efflux to the seed apoplast. The expression of SuSy in cotyledons also suggests a role in protein and lipid synthesis. In summary, the developing cotton seed provides an excellent example of the diverse roles played by SuSy in carbon metabolism.

New Insights into Roles of Cell Wall Invertase in Early Seed Development Revealed by Comprehensive Spatial and Temporal Expression Patterns of GhCWIN1 in Cotton

“…As the seed develops to 10 DAA, the seed coat TCPs begin to develop intensive WIs, thereby forming functional TCs (Ruan et al, 1997;Pugh et al, 2010). Inside this layer, multicellular proembryo gave rise to globular stage embryo and the endosperm has undergone the cellularization process starting from the micropylar end to the chalazal region ( Fig.…”

“…B, At the globular embryo stage, GhCWIN1 expression became undetectable in the seed coat. Suc is degraded by Sus at the innermost layer of the seed coat for TC WIs (Ruan et al, 1997;Pugh et al, 2010) or moved toward the filial tissues mediated by Suc transporters (Ruan et al, 2001). Suc is cleaved by Sus in the cellularizing endosperm for cell wall biosynthesis (cellularization; Ruan et al, 2008).…”

“…Total RNA was isolated from five cotton seeds and other specified tissues according to Ruan et al (1997). First-strand cDNA was synthesized using the SMART RACE cDNA Amplification Kit (Clontech), following the manufacturer's instructions.…”

“…In cotton seed, Suc is unloaded from phloem in outer seed coat and delivered outward to seed epidermis for fiber growth and inward to filial tissues (Ruan et al, 1997). At approximately 10 d after anthesis (DAA), the innermost layer of cotton seed coat develops into transfer cells (TCs) with invaginated cell wall ingrowths (WIs), which facilitate the efflux of nutrient to developing endosperm and embryo (Pugh et al, 2010).…”

Unraveling mechanisms of cell expansion linking solute transport, metabolism, plasmodesmtal gating and cell wall dynamics

“…13 In elongating fibers, of sucrose. 12 While collective expression level of GhSus gene members appears to be strong throughout the fiber elongation period 15 ( Fig. 1), GhVIN1, a major vacuolar invertase in cotton fiber, shows evidently higher expression level early in fiber elongation (0-10 DAA) matching high VIN activity observed in this stage.…”