Cytosolic invertases contribute to cellulose biosynthesis and influence carbon partitioning in seedlings of Arabidopsis thaliana

Abstract

In plants, UDP-glucose is the direct precursor for cellulose biosynthesis, and can be converted into other NDP-sugars required for the biosynthesis of wall matrix polysaccharides. UDP-glucose is generated from sucrose by two distinct metabolic pathways. The first pathway is the direct conversion of sucrose to UDP-glucose and fructose by sucrose synthase. The second pathway involves sucrose hydrolysis by cytosolic invertase (CINV), conversion of glucose to glucose-6-phosphate and glucose-1-phosphate, and UDP-glucose generation by UDP-glucose pyrophosphorylase (UGP). Previously, Barratt et al. (Proc. Natl Acad. Sci. USA, 106, 2009 and 13124) have found that an Arabidopsis double mutant lacking CINV1 and CINV2 displayed drastically reduced growth. Whether this reduced growth is due to deficient cell wall production caused by limited UDP-glucose supply, pleiotropic effects, or both, remained unresolved. Here, we present results indicating that the CINV/UGP pathway contributes to anisotropic growth and cellulose biosynthesis in Arabidopsis. Biochemical and imaging data demonstrate that cinv1 cinv2 seedlings are deficient in UDP-glucose production, exhibit abnormal cellulose biosynthesis and microtubule properties, and have altered cellulose organization without substantial changes to matrix polysaccharide composition, suggesting that the CINV/UGP pathway is a key metabolic route to UDP-glucose synthesis in Arabidopsis. Furthermore, differential responses of cinv1 cinv2 seedlings to exogenous sugar supplementation support a function of CINVs in influencing carbon partitioning in Arabidopsis. From these data and those of previous studies, we conclude that CINVs serve central roles in cellulose biosynthesis and carbon allocation in Arabidopsis.

Secondary cell wall biosynthesis

“…Although early studies on cellulose biosynthesis in cotton fibers suggested a role for sucrose synthase‐mediated supply of UDP‐Glc in cellulose biosynthesis (Haigler et al ., ), genetic analysis in both Arabidopsis and aspen showed little effect of mutations or downregulation of sucrose synthase genes on cellulose synthesis and plant growth, indicating that sucrose synthases are unlikely to play a major role in supplying UDP‐Glc for cellulose synthesis (Barratt et al ., ; Gerber et al ., ). By contrast, simultaneous mutations of two Arabidopsis cytosolic invertase genes cause severe growth defects (Barratt et al ., ) and further biochemical and imaging analyses revealed a deficiency in the production of UDP‐Glc and cellulose and an alteration in cellulose microfibril organization (Barnes & Anderson, ). Downregulation of a wood‐associated cytosolic invertase gene in aspen also leads to a reduction in the amount of crystalline cellulose and UDP‐Glc in the wood of transgenic aspen (Rende et al ., ).…”

Emerging Functions for Cell Wall Polysaccharides Accumulated during Eudicot Seed Development

“…In Arabidopsis, the importance of cellulose synthesis for secondary wall thickening of seed coat epidermal cells was confirmed by the observation of reduced radial wall reinforcement in single and mutant combinations affected in cellulose synthase catalytic subunits CESA9 , CESA2 and CESA5 [51,52]. Similar defects have also been observed for cinv1 cinv2 , defective for cytosolic invertases that generate UDP-glucose substrates for cellulose synthesis [53]. The precise function of the radial wall reticulations observed on Arabidopsis seeds remains to be determined, together with that of the intriguing central columella.…”

Vacuolar sucrose homeostasis is critical for development, seed properties and survival of dark phases of Arabidopsis

“…Barnes and Anderson, 2018), pointing to a synergistic function of both invertase 567 isoforms (cytosolic and vacuolar) for carbon supply under conditions of low energy.568 Thus, our data raised on amiR vi1-2 seedlings explain how glucose is released into 569 the cytosol of etiolated plants. Obviously, sufficient vacuolar invertase activity is 570 required for Arabidopsis development under dark conditions, in which an efficient 571 conversion of stored lipids into energy providing sugars is mandatory.…”