Journal
PLANT JOURNAL
Volume 109, Issue 6, Pages 1441-1456Publisher
WILEY
DOI: 10.1111/tpj.15640
Keywords
pectin; plant cell wall; biosynthesis; GAUT; galacturonosyltransferase; glycosyltransferase; polysaccharide synthesis; biosynthesis; initiation; galacturonan; Arabidopsis thaliana
Categories
Funding
- BioEnergy Science Center (BESC) [DE-PS02-06ER64304]
- Center for Bioenergy Innovation (CBI)
- Department of Energy [DE-SC0015662, DE-FG02-93ER20097]
- National Institutes of Health [P41GM103390, P01GM107012]
- Office of Biological and Environmental Research in the Department of Energy's Office of Science
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Homogalacturonan (HG) is a crucial pectic glycan in plant growth, development, and defense against pathogens, synthesized by members of the GALACTURONOSYLTRANSFERASE (GAUT) family. Different GAUT members exhibit varying levels of HG:GalAT activity, with GAUT13 and GAUT14 showing unique de novo HG synthesis capabilities.
Homogalacturonan (HG), the most abundant pectic glycan, functions as a cell wall structural and signaling molecule essential for plant growth, development and response to pathogens. HG exists as a component of pectic homoglycans, heteroglycans and glycoconjugates. HG is synthesized by members of the GALACTURONOSYLTRANSFERASE (GAUT) family. UDP-GalA-dependent homogalacturonan:galacturonosyltransferase (HG:GalAT) activity has previously been demonstrated for GAUTs 1, 4 and 11, as well as the GAUT1:GAUT7 complex. Here, we show that GAUTs 10, 13 and 14 are also HG:GalATs and that GAUTs 1, 10, 11, 13, 14 and 1:7 synthesize polymeric HG in vitro. Comparison of the in vitro HG:GalAT specific activities of the heterologously-expressed proteins demonstrates GAUTs 10 and 11 with the lowest, GAUT1 and GAUT13 with moderate, and GAUT14 and the GAUT1:GAUT7 complex with the highest HG:GalAT activity. GAUT13 and GAUT14 are also shown to de novo synthesize (initiate) HG synthesis in the absence of exogenous HG acceptors, an activity previously demonstrated for GAUT1:GAUT7. The rate of de novo HG synthesis by GAUT13 and GAUT14 is similar to their acceptor dependent HG synthesis, in contrast to GAUT1:GAUT7 for which de novo synthesis occurred at much lower rates than acceptor-dependent synthesis. The results suggest a unique role for de novo HG synthesis by GAUTs 13 and 14. The reducing end of GAUT13-de novo-synthesized HG has covalently attached UDP, indicating that UDP-GalA serves as both a donor and acceptor substrate during de novo HG synthesis. The functional significance of unique GAUT HG:GalAT catalytic properties in the synthesis of different pectin glycan or glycoconjugate structures is discussed.
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