Analysis of a xyloglucan endotransglycosylase/hydrolase (XTH) from the lycopodiophyte Selaginella kraussiana suggests that XTH sequence characteristics and function are highly conserved during the evolution of vascular plants

Abstract

A tissue print followed by a xyloglucan endotransglycosylase assay revealed that XET activity is present at sites of cell elongation in both roots and shoots of the lycopodiophyte Selaginella kraussiana. This paper provides the first report and analysis of a xyloglucan endotransglycosylase/hydrolase (XTH) cDNA sequence, isolated from a club moss. In silico analysis of the deduced amino acid sequence revealed a strong conservation of the XET-domain described in higher plants. The catalytic site (DEIDLEFLG) varies in only one amino acid compared with the consensus sequence and was shown to be functional after recombinant expression of Sk-XTH1 in Pichia pastoris. Sk-XTH1 displays xyloglucan endotransglycosylase activity over a broad pH (4.5-7.5) and temperature range (4-30 degrees C), but it shows no hydrolase activity. The catalytic site is followed by a consensus sequence for N-linked glycosylation. Four terminal cysteines were shown to stabilize a putative XET-C terminal extension region, which includes conserved amino acids, involved in the recognition and binding of the substrates. The N-linked sugar interactions as well as the disulphide bridges were shown to be necessary to perform XET activity. The presence of a highly conserved XTH sequence and function in a microphyllophyte suggests that XTHs were present before the divergence of lycopodiophytes and euphyllophytes. It also points to a possible key role for XTHs in the production of a cell wall that allowed the further evolution of land plants.

Xyloglucan endotransglucosylase and cell wall extensibility

“…These results provide evidence that XTHs from group I are mainly involved in the restructuring of the cell wall during growth and development, as suggested by Van Sandt et al, 2006, but they are not the limiting factor for plant growth, although XTHs has been considered as primarily cell wall loosening agents.…”

Characterization of two partially purified xyloglucan endotransglycosylases from parsley (Petroselinum crispum) roots

“…Slight indication of hydrolytic activity was considered as a result of formation of enzyme-substrate complex rather than XEH activity (Van Sandt et al 2006). Several enzymes have been described having both XEH and XET activity as in nasturtium (Edwards et al 1986;Farkaš et al 1992;de Silva et al 1993;Fanutti et al 1993Fanutti et al , 1996Steele et al 2001;Sulová et al 2003;Chanliaud et al 2004), ripe kiwifruit (Schröder et al 1998) or exclusively endohydrolytic activity as in azuki bean epicotyls (Tabuchi et al 2001).…”

“…XET activity has been detected in vivo in a wide variety of plants and tissues (Vissenberg et al 2000(Vissenberg et al , 2003Bourquin et al 2002;Fry 2004;Van Sandt et al 2006). Plant extracts usually contain multiple forms of XET (Farkaš et al 2005).…”

“…Some of them had a relatively sharp pH optimum at 5.0-5.5 (Schröder et al 1998;Steele & Fry 2000;Saura-Valls et al 2006) and the others at ∼6.5 (Steele & Fry 2000). However, there is a group of XETs, which exhibit a broad pH optimum such as enzyme from nasturtium seeds and Selaginella krasiana (Van Sandt et al 2006) or some forms of XET from mung bean seedlings (Steele & Fry 2000). This fact may suggest action not only in the primary cell wall but in different sub-cellular locations, possibly including endo-membrane vesicles during the transport of XGs from their site of synthesis in Golgi bodies to their destination in the wall (Steele & Fry 2000).…”

“…This fact may suggest action not only in the primary cell wall but in different sub-cellular locations, possibly including endo-membrane vesicles during the transport of XGs from their site of synthesis in Golgi bodies to their destination in the wall (Steele & Fry 2000). In addition, the broad pH optimum allows the enzyme to be active in a wide range of physiological conditions (Van Sandt et al 2006).…”