The targeting of starch binding domains from starch synthase III to the cell wall alters cell wall composition and properties

Abstract

Starch binding domains of starch synthase III from Arabidopsis thaliana (SBD123) binds preferentially to cell wall polysaccharides rather than to starch in vitro. Transgenic plants overexpressing SBD123 in the cell wall are larger than wild type. Cell wall components are altered in transgenic plants. Transgenic plants are more susceptible to digestion than wild type and present higher released glucose content. Our results suggest that the transgenic plants have an advantage for the production of bioethanol in terms of saccharification of essential substrates. The plant cell wall, which represents a major source of biomass for biofuel production, is composed of cellulose, hemicelluloses, pectins and lignin. A potential biotechnological target for improving the production of biofuels is the modification of plant cell walls. This modification is achieved via several strategies, including, among others, altering biosynthetic pathways and modifying the associations and structures of various cell wall components. In this study, we modified the cell wall of A. thaliana by targeting the starch-binding domains of A. thaliana starch synthase III to this structure. The resulting transgenic plants (E8-SDB123) showed an increased biomass, higher levels of both fermentable sugars and hydrolyzed cellulose and altered cell wall properties such as higher laxity and degradability, which are valuable characteristics for the second-generation biofuels industry. The increased biomass and degradability phenotype of E8-SBD123 plants could be explained by the putative cell-wall loosening effect of the in tandem starch binding domains. Based on these results, our approach represents a promising biotechnological tool for reducing of biomass recalcitrance and therefore, the need for pretreatments.

Advances in molecular engineering of carbohydrate-binding modules

“…Low‐lignin rice was developed through the expression of a laccase‐cellulose‐binding domain (CBD) fusion protein, and this protein increases saccharification efficiency (up to 1.5‐fold) and modifications in the cell wall composition . Similarly, changes in the cell wall composition of Arabidopsis thaliana plants can be achieved through overexpression of the starch‐binding domain (SBD123) of A. thaliana starch synthase III, which increases the cell wall degradability while increasing biomass, resulting in higher levels of fermentable sugars and hydrolyzed cellulose …”

“…80 Similarly, changes in the cell wall composition of Arabidopsis thaliana plants can be achieved through overexpression of the starch-binding domain (SBD123) of A. thaliana starch synthase III, which increases the cell wall degradability while increasing biomass, resulting in higher levels of fermentable sugars and hydrolyzed cellulose. 81 Four tandem proteins, comprising two CBMs, have been used in the paper industry. 35 The CBM3-CBM3 protein shows promising potential for the paper industry because it can enhance the mechanical properties of paper, such as folding endurance (27.4%) and tensile strength (15.5%).…”

Engineering of Bioenergy Crops: Dominant Genetic Approaches to Improve Polysaccharide Properties and Composition in Biomass

“…The average cell area was increased by 40% and dry biomass weight by 76%. Unlike the ClEXPA-expressing plants, Grisolia et al (2017) observed a 27% reduction in cell wall thickness and similar amounts of cellulose in transgenic Arabidopsis stems. This suggests SBD123 loosened the components of the cell wall, stretching the cell wall to cover a greater cell volume.…”

“…It is also interesting to explore the effects that CBMs alone can have on cell wall architecture. In Arabidopsis, the coding sequence of the CBM of Starch Synthase III (SSIII) was overexpressed and targeted to the cell wall (Grisolia et al, 2017). Though starch and cellulose are very different in structure, previous work indicated that the concatenated triplicate of CBMs (collectively referred to as SBD123) from SSIII had preferential affinity for the linear portions of the starch molecule.…”

Dependence of physiochemical, functional and textural properties of high‐resistant starch rice on endogenous nonstarch polysaccharides

“…For AAC, there were no significant differences between the different treatments of R7954. While there was significant increase ( P < 0.05) after treatment with three enzymes altogether in cw , which might be because of high amylose content and the amylose may interact with NSPs such as pectin and cellulose do (Grisolia et al ., ), and was released by removal by hydrolysis of NSPs, the significant decreases in TDF ( P < 0.01) and small changes in starch content suggested that treatment with cellulase, hemicellulose and pectinase was effective with only minor changes in starch content.…”