Fig 1.
Structure of RG-II and diester linkages with boron.
The RG-II dimer is formed by ester bonds between a boron atom and the apiosyl residues of side chain A. The grey part of the side chain A is absent in mur1-1 RG-II, a defect that leads to a reduced RG-II dimer formation [13],[14]. Rha: rhamnose; Fuc: fucose; Araf: arabinofuranose; Ara: arabinopyranose; Ace: aceric acid; GalA: galacturonic acid; Gluc: glucuronic acid; Api: apiose; Dha: 2-keto-3-deoxy-D-lyxo-heptulosaric acid; Kdo: 2-keto-3-deoxy-D-manno-octulosonic acid; Gal: galactose; Xyl: xylose.
Table 1.
Impact of the MUR1 mutation on the dry weight and lignin content of mature inflorescence stems.
Table 2.
Monosaccharide composition of alcohol insoluble residue isolated from mature stems.
Table 3.
Determination of thioacidolysis monomers released from extractive-free mature stems.
Fig 2.
Gene coexpression network made from genes up-regulated in mur1-1 stems.
An edge weighted, force-directed approach was used, based on data retrieved from ATTED-II and visualised in Cytoscape 2.8 (http://www.cytoscape.org). In this network, each gene is represented by a node and each grey edge connecting two nodes represents a mutual rank <100. Two modules of high density were revealed suggesting a tight coexpression. Green and orange edges link MYB73 and DDP1 respectively to secondary cell wall genes potentially regulated by these transcription factors (Taylor-Teeples et al., 2014).
Fig 3.
Inflorescence cross sections at intermediate and mature stages of development.
Cross sections through the basal region of the infloresence stem for wild type (A) and mur1-1 (B,D) at an intermediate stage of development. Cross sections of the basal region of the stem of mur1-1 at a mature stage of development (C,E) stained with phloroglucinol-HCl or with the Maüle reagent (F). Phloem sclereids are encircled on D and E and abnormal lignified cells rich in aldehyde compounds are indicated by black arrows. The pitted cell wall of regenerative xylem and the fragmentation of the sclerenchyma cylinder are indicated by black arrow heads and dotted arrows respectively. The cortex cell wall layer are indicated by asterisks. Observation of the perforation plate of a regenerative xylem cell observed by confocal microscopy (G). Ep: epidermis, co: cortex, ph: phloem, xy: xylem, Sxy: secondary xylem, Rxy: regenerative xylem, if: interfascicular fibers.
Fig 4.
Bor1-3 mutants have enhanced secondary growth and regenerative xylem.
Basal cross-sections of primary inflorescence stained with phloroglucinol-HCl of bor1-3 (A,C and D) and wild type (B). Phloem sclereids are encircled in A. ph: phloem, xy: xylem, Sxy: secondary xylem, Rxy: regenerative xylem, if: interfascicular fibers.
Fig 5.
Putative mechanisms responsible for the mur1-1 phenotype in the inflorescence stem.
A. Diagram of cell adhesion deficiency at the edge of lignified tissues and non-lignified cortex cells in mur1-1. RG-II dimers are enriched in the cell corners. Relative sizes of middle lamella, primary and secondary cell walls are not drawn to scale. B. Working hypothesis of regenerative xylem formation in the mur1-1 inflorescence stem. The cell adhesion is compromised by reduced RG-II cross linking. Mechanical stress on cortex and lignified tissues induces loss of cell adhesion and then transcription of jasmonate related genes. Regenerative elements are formed by activation of specific transcription factors. Co: cortex, ph: phloem, xy: xylem, Rxy: regenerative xylem, if: interfascicular fibers. Blue arrows: shear forces.