Overexpression of the carbohydrate binding module of strawberry expansin2 in Arabidopsis thaliana modifies plant growth and cell wall metabolism
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Several cell wall enzymes are carbohydrate active enzymes that contain a putative Carbohydrate Binding Module (CBM) in their structures. The main function of these non-catalitic modules is to facilitate the interaction between the enzyme and its substrate. Expansins are non-hydrolytic proteins present in the cell wall, and their structure includes a CBM in the C-terminal that bind to cell wall polymers such as cellulose, hemicelluloses and pectins. We studied the ability of the Expansin2 CBM (CBMFaEXP2) from strawberry (Fragaria x ananassa, Duch) to modify the cell wall of Arabidopsis thaliana. Plants overexpressing CBMFaEXP2 were characterized phenotypically and biochemically. Transgenic plants were taller than wild type, possibly owing to a faster growth of the main stem. Cell walls of CBMFaEXP2-expressing plants were thicker and contained higher amount of pectins. Lower activity of a set of enzymes involved in cell wall degradation (PG, β-Gal, β-Xyl) was found, and the expression of the corresponding genes (AtPG, Atβ-Gal, Atβ-Xyl5) was reduced also. In addition, a decrease in the expression of two A. thaliana Expansin genes (AtEXP5 and AtEXP8) was observed. Transgenic plants were more resistant to Botrytis cinerea infection than wild type, possibly as a consequence of higher cell wall integrity. Our results support the hypothesis that the overexpression of a putative CBM is able to modify plant cell wall structure leading to modulation of wall loosening and plant growth. These findings might offer a tool to controlling physiological processes where cell wall disassembly is relevant, such as fruit softening.
KeywordsA. thaliana Carbohydrate binding module Cell wall Expansin Pectin Strawberry
This work was supported by Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Agencia Nacional de Promoción Científica y Tecnológica (ANPCyT), Universidad Nacional de La Plata (UNLP), Universidad Nacional de San Martín (UNSAM) and Ministerio de Ciencia, Tecnología e Innovación Productiva (MINCyT). Authors thank to José Luis Burgos (CIC Pcia. Bs. As, Argentina) for his valuable technical assistance.
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