Premium
Another building block in the plant cell wall: Barley xyloglucan xyloglucosyl transferases link covalently xyloglucan and anionic oligosaccharides derived from pectin
Author(s) -
Stratilová Barbora,
Šesták Sergej,
Mravec Jozef,
Garajová Soňa,
Pakanová Zuzana,
Vadinová Kristína,
Kučerová Danica,
Kozmon Stanislav,
Schwerdt Julian G.,
Shirley Neil,
Stratilová Eva,
Hrmova Maria
Publication year - 2020
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/tpj.14964
Subject(s) - xyloglucan , hordeum vulgare , chemistry , glycoside hydrolase , biochemistry , glycosyltransferase , cell wall , mutant , stereochemistry , enzyme , gene , biology , botany , poaceae
SUMMARY We report on the homo‐ and hetero‐transglycosylation activities of the HvXET3 and HvXET4 xyloglucan xyloglucosyl transferases (XET; EC 2.4.1.207) from barley ( Hordeum vulgare L.), and the visualisation of these activities in young barley roots using Alexa Fluor 488‐labelled oligosaccharides. We discover that these isozymes catalyse the transglycosylation reactions with the chemically defined donor and acceptor substrates, specifically with the xyloglucan donor and the penta‐galacturonide [α(1‐4)GalA p ] 5 acceptor – the homogalacturonan (pectin) fragment. This activity is supported by 3D molecular models of HvXET3 and HvXET4 with the docked XXXG donor and [α(1‐4)GalA p ] 5 acceptor substrates at the −4 to +5 subsites in the active sites. Comparative sequence analyses of barley isoforms and seed‐localised TmXET6.3 from nasturtium ( Tropaeolum majus L.) permitted the engineering of mutants of TmXET6.3 that could catalyse the hetero‐transglycosylation reaction with the xyloglucan/[α(1‐4)GalA p ] 5 substrate pair, while wild‐type TmXET6.3 lacked this activity. Expression data obtained by real‐time quantitative polymerase chain reaction of HvXET transcripts and a clustered heatmap of expression profiles of the gene family revealed that HvXET3 and HvXET6 co‐expressed but did not share the monophyletic origin. Conversely, HvXET3 and HvXET4 shared this relationship, when we examined the evolutionary history of 419 glycoside hydrolase 16 family members, spanning monocots, eudicots and a basal Angiosperm. The discovered hetero‐transglycosylation activity in HvXET3 and HvXET4 with the xyloglucan/[α(1‐4)GalA p ] 5 substrate pair is discussed against the background of roles of xyloglucan‐pectin heteropolymers and how they may participate in spatial patterns of cell wall formation and re‐modelling, and affect the structural features of walls.