The role of COBRA‐LIKE 2 function, as part of the complex network of interacting pathways regulating Arabidopsis seed mucilage polysaccharide matrix organization

Abstract

The production of hydrophilic mucilage along the course of seed coat epidermal cell differentiation is a common adaptation in angiosperms. Previous studies have identified COBRA-LIKE 2 (COBL2), a member of the COBRA-LIKE gene family, as a novel component required for crystalline cellulose deposition in seed coat epidermal cells. In recent years, Arabidopsis seed coat epidermal cells (SCEs), also called mucilage secretory cells, have emerged as a powerful model system for the study of plant cell wall components biosynthesis, secretion, assembly and de muro modification. Despite accumulating data, the molecular mechanism of COBL function remains largely unknown. In the current research, we utilized genetic interactions to study the role of COBL2 as part of the protein network required for seed mucilage production. Using correlative phenotyping of structural and biochemical characteristics, unique features of the cobl2 extruded mucilage are revealed, including: 'unraveled' ray morphology, loss of primary cell wall 'pyramidal' organization, reduced Ruthenium red staining intensity of the adherent mucilage layer, and increased levels of the monosaccharides arabinose and galactose. Examination of the cobl2cesa5 double mutant provides insight into the interface between COBL function and cellulose deposition. Additionally, genetic interactions between cobl2 and fei1fei2 as well as between each of these mutants to mucilage-modified 2 (mum2) suggest that COBL2 functions independently of the FEI-SOS pathway. Altogether, the presented data place COBL2 within the complex protein network required for cell wall deposition in the context of seed mucilage and introduce new methodology expending the seed mucilage phenotyping toolbox.

Role for Arabidopsis PLC7 in Stomatal Movement, Seed Mucilage Attachment, and Leaf Serration

“…In addition, cellulosic rays stained with calcofluor white and pontamine S4B appear shorter around the mutant seeds. These defects have been reported in mutants that disrupt cellulose synthesis ( Mendu et al, 2011 ; Sullivan et al, 2011 ; Griffiths et al, 2015 ; Griffiths and North, 2017 ; Ben-Tov et al, 2018 ), as well as in mutants that directly impair the synthesis of xylan ( Voiniciuc et al, 2015a , b ; Hu, 2016 ; Hu et al, 2016 ; Ralet et al, 2016 ). Therefore, PLC could influence membrane phospholipids that are important for the trafficking of cellulose synthase enzymes or the secretion of matrix polysaccharides (such as xylan) from the Golgi apparatus.…”

“…Increased solubility of the pectins has been linked to perturbation of cellulose deposition ( Basu et al, 2016 ; Ben-Tov et al, 2018 ). To test this, wild type- and plc5/7 seeds were stained with Calcofluor White (CFW, for cellulose and other β-glucans staining; (Figure 3C , left panel) or Pontamine S4B (cellulose-specific dye; Figure 3C , right panel) ( Anderson et al, 2010 ; Wallace and Anderson, 2012 ).…”

Initial responses of the trap‐crop, Solanum sisymbriifolium, to Globodera pallida invasions

“…Homologues of this protein transport cutin monomers to the epidermis of root cells in Arabidopsis to reduce water loss and repair breaks in the protective wax layer (Panikashvili et al., 2007). At the same time, nematodes also induced a COBRA ‐like membrane‐associated sensory protein similar to a protein that is responsible for regulating cellulose deposition and mucilage production in other species (Ben‐Tov et al., 2018). The nematode‐specific set of sequences also included Ssi006463 and Ssi047837.…”

Seed hemicelluloses tailor mucilage properties and salt tolerance

“…Before the discovery of the minor mucilage components, Arabidopsis seed mucilage was thought to be mainly shaped by pectin content or gelling ability. Biochemical and histological analyses of double mutants have clarified how SOS5 and cellulosic ray-like structures provide two distinct mechanisms to anchor pectin to seeds (Griffiths et al, 2014(Griffiths et al, , 2016Ben-Tov et al, 2018). However, the functional roles of the highly branched xylan and HM found in mucilage have yet to be evaluated in detail.…”