Table 1 Compact overview of modifications of P4H, GLCAT, and GH43 activities in Arabidopsis thaliana and their effects observed at molecular, cellular, and organ levels
From: Review: structure and modifications of arabinogalactan proteins (AGPs)
Modification type/gene modulation | Modification effect | Ref. | |||
|---|---|---|---|---|---|
molecular level | cellular level | organ/organism level | |||
P4H mutants SlP4H1 SlP4H7 SlP4H9 AtP4Hs | gene down-regulation | • tissue-specific expression • inactivity of P4Hs • inhibition of hydroxylation process • lower extent for AGP substrate | • localization in punctuated compartments (the Golgi stacks) • reduced Hyp content in root cell walls • changes in extensins level | • reduced root hairs length • reduced root hairs density • lower level of adaptation to hypoxia and anoxia conditions | |
gene overexpression | • up-regulation of P4H activity • higher expression of genes associated with hypoxia | • alters in the cell wall assembly • different fibrils orientation | • increased rate of root hairs elongation • increased density of root hairs • increased plant biomass | ||
GLCAT mutants GLCAT14A GLCAT14B GLCAT14C GLCAT14D GLCAT14E | gene down-regulation | • formation of premature STOP codons • lack of GLCAT activity • changes in AGP glycan biosynthesis • increased Gal and Ara in AGPs | • increased AGP content in specific plant organs (silique, leaf rosettes, stems, pods) • reduced amount of GlcA in cell wall • reduced Ca2+ binding • abnormal structure of the primary cell wall | • delayed seed germination and hypersensitivity to the stratification conditions • defective non-germinating pollen grain • reduced root hairs length • reduced plant height • reduction in adherent seed mucilage | [80] |
gene down-regulation | • lack of GLCAT activity • defective synthesis of AGs • reduction of glucuronidation of AGs • elongation of the branched β-1,3- and β-1,6-galactan | • significant reduced Ca2+ binding capacity of AGPs (in comparison to the higher-order mutants and WT) • changes in intracellular Ca2+ transient signals • perturbed calcium waves in roots | • smaller trichomes and branching defect • crooked seedlings • shorter inflorescences • etiolated hypocotyl phenotype • limited seedling growth • plant growth deficiencies | [81] | |
GH43 mutants GH43A GH43B | gene down-regulation | • lack of GH43 β-1,3-galactosidase activity • inaccessible of β-1,3-linkages • disruption in the glycosylation process • changes in AGP glycan biosynthesis | • changes in the abundance of cell wall-associated AGPs • alters in the cell wall extensibility • stronger binding of certain AGPs to the cell wall • changes in pectin content (HG, RGI) • changes in cell wall polymer deposition | • root cell expansion defects • loss of anisotropic root growth • swelling of the root epidermis cells | [84] |