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Suppression of Arabidopsis GGLT 1 affects growth by reducing the L‐galactose content and borate cross‐linking of rhamnogalacturonan‐ II
Author(s) -
Sechet Julien,
Htwe Soe,
Urbanowicz Breeanna,
Agyeman Abigail,
Feng Wei,
Ishikawa Toshiki,
Colomes Marianne,
Kumar Kavitha Satish,
KawaiYamada Maki,
Dinneny José R.,
O'Neill Malcolm A.,
Mortimer Jenny C.
Publication year - 2018
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.14088
Subject(s) - biology , galactose , cell wall , biochemistry , mutant , gene
Summary Boron is a micronutrient that is required for the normal growth and development of vascular plants, but its precise functions remain a subject of debate. One established role for boron is in the cell wall where it forms a diester cross‐link between two monomers of the low‐abundance pectic polysaccharide rhamnogalacturonan‐ II ( RG ‐ II ). The inability of RG ‐ II to properly assemble into a dimer results in the formation of cell walls with abnormal biochemical and biomechanical properties and has a severe impact on plant productivity. Here we describe the effects on RG ‐ II structure and cross‐linking and on the growth of plants in which the expression of a GDP ‐sugar transporter ( GONST 3/ GGLT 1) has been reduced. In the GGLT 1 ‐silenced plants the amount of L‐galactose in side‐chain A of RG ‐ II is reduced by up to 50%. This leads to a reduction in the extent of RG ‐ II cross‐linking in the cell walls as well as a reduction in the stability of the dimer in the presence of calcium chelators. The silenced plants have a dwarf phenotype, which is rescued by growth in the presence of increased amounts of boric acid. Similar to the mur1 mutant, which also disrupts RG ‐ II cross‐linking, GGLT 1 ‐silenced plants display a loss of cell wall integrity under salt stress. We conclude that GGLT 1 is probably the primary Golgi GDP ‐L‐galactose transporter, and provides GDP ‐L‐galactose for RG ‐ II biosynthesis. We propose that the L‐galactose residue is critical for RG ‐ II dimerization and for the stability of the borate cross‐link.