Overexpression of a Potato Sucrose Synthase Gene in Cotton Accelerates Leaf Expansion, Reduces Seed Abortion, and Enhances Fiber Production

Abstract

Sucrose synthase (Sus) is a key enzyme in the breakdown of sucrose and is considered a biochemical marker for sink strength, especially in crop species, based on mutational and gene suppression studies. It remains elusive, however, whether, or to what extent, increase in Sus activity may enhance sink development. We aimed to address this question by expressing a potato Sus gene in cotton where Sus expression has been previously shown to be critical for normal seed and fiber development. Segregation analyses at T1 generation followed by studies in homozygous progeny lines revealed that increased Sus activity in cotton (1) enhanced leaf expansion with the effect evident from young leaves emerging from shoot apex; (2) improved early seed development, which reduced seed abortion, hence enhanced seed set, and (3) promoted fiber elongation. In young leaves of Sus overexpressing lines, fructose concentrations were significantly increased whereas, in elongating fibers, both fructose and glucose levels were increased. Since hexoses contribute little to osmolality in leaves, in contrast to developing fibers, it is concluded that high Sus activity promotes leaf development independently of osmotic regulation, probably through sugar signaling. The analyses also showed that doubling the Sus activity in 0-d cotton seeds increased their fresh weight by about 30%. However, further increase in Sus activity did not lead to any further increase in seed weight, indicating an upper limit for the Sus overexpression effect. Finally, based on the observed additive effect on fiber yield from increased fiber length and seed number, a new strategy is proposed to increase cotton fiber yield by improving seed development as a whole, rather than solely focusing on manipulating fiber growth.

Critical Roles of Vacuolar Invertase in Floral Organ Development and Male and Female Fertilities Are Revealed through Characterization of GhVIN1-RNAi Cotton Plants

“…Prior to its use for metabolism and biosynthesis, Suc needs to be degraded into hexoses by either Suc synthase (Sus; EC 2.4.1.13) or invertase (INV; EC 3.2.1.26). Sus cleaves Suc in the presence of UDP into UDP-Glc and Fru and is largely involved in cell wall and starch biosynthesis in sink organs (Brill et al, 2011) and maintaining sink strength (Pozueta-Romero et al, 1999;Xu et al, 2012), especially in crop species (Ruan, 2014). INV, on the other hand, hydrolyzes Suc into Fru and Glc and plays essential roles in plant development and stress responses (Koch, 2004;Ruan, 2014).…”

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

“…Prior to its use for metabolism and biosynthesis, Suc must be degraded into hexoses, by either Suc synthase (Sus; EC 2.4.1.13) or invertase (b-fructosidase; EC 3.2.1.26). Sus cleaves Suc into UDP-Glc and Fru and is largely involved in cell wall and starch biosynthesis (Chourey et al, 1998;Brill et al, 2011) and maintaining sink strength (Pozueta-Romero et al, 1999;Xu et al, 2012). Invertase, on the other hand, irreversibly hydrolyzes Suc into Fru and Glc and plays vital roles in plant development and stress responses Li et al, 2012).…”

Recent progress toward understanding the role of starch biosynthetic enzymes in the cereal endosperm

“…For a summary of the transporters found from the plastid envelope membrane, see [18]. SuSyoverexpressed cotton plants have an increase of biomass and fibre yield [19,20], while maize sh1 mutants possessing approximately 10% of the wild-type SuSy activity show a substantial (~50-70%) reduction in starch levels in the seed endosperm [16,21]. The SuSy activity is known to be regulated by reversible phosphorylation, possibly by a seed-development specific protein kinase (SPK) [22].…”

“…It starts with individual chains as the first level, which are formed by ADP-glucose through (1→4)-α-glycosidic linkages. Those chains in amylopectin have been further denoted as C chains having the reducing end, A chains (degree of polymerization, DP, [6][7][8][9][10][11][12] carrying no branches, B1 chains (DP [13][14][15][16][17][18][19][20][21][22][23][24] carrying A chains, B2 chains (DP DOI 10.1515/amylase-2017-0006 [25][26][27][28][29][30][31][32][33][34][35][36] carrying B1 chains, B3 chains (DP > 36) carrying B2 chains, and so on (for a recent review, see [2]). Although still occasionally one finds statements to the contrary, amylose is not solely linear, but contains a small but significant number of long-chain branches [3].…”