Torode, T. A. | Search bioRxiv

bioRxiv2019

On Pectin Methyl-esterification: Implications for In vitro and In vivo Viscoelasticity

Pectin is a major component of the primary plant cell wall and is important for cell expansion. However, the relationship between its chemistry and mechanical properties is not fully understood, especially in vivo. In this study, a protocol for viscoelastic micro-indentation using atomic force microscopy (AFM) was developed and applied to pectin in vitro and in vivo. After determining that linear viscoelasticity was a suitable theoretical framework for in vitro pectin analyses were conducted with both a standard linear solid and fractional Zener model. These indicated a strong coupling between elastic and viscous properties over a range of degrees of methyl-esterification (DM). Both elasticity and viscosity were found to vary non-linearly with DM which had interesting consequences for pectin gels of mixed DM. In Arabidopsis cell walls, the standard linear solid model was found to be appropriate. In this in vivo composite material a weaker elastic-viscous coupling was exhibited, correlated with DM. The viscoelastic testing in vivo of rapidly elongating cell walls, rich in high DM pectin, displayed a longer viscous time-scale. The implications of the testing method and results are discussed in the context of mechanobiology, mechano-chemistry, and cell growth.

plant biology↗

bioRxiv2018

Glycerol phosphate acyltransferase 6 controls filamentous pathogen interactions and cell wall properties of the tomato and Nicotiana benthamiana leaf epidermis

The leaf epidermal wall is covered by a cuticle, composed of cutin and waxes, which protects against dehydration and constitutes a barrier against pathogen attack. Cutin monomers are formed by the transfer of 16- or 18-carbon fatty acids to glycerol by glycerol-3-phosphate acyltransferase (GPAT) enzymes, which facilitates their transport to the plant surface. Here we address the dual functionality of pathogen-inducible Glycerol phosphate acyltransferase 6 (GPAT6) in controlling pathogen entry and dehydration in leaves. Silencing of Nicotiana benthamiana NbGPAT6a increased leaf susceptibility to the oomycetes Phytophthora infestans and P. palmivora, whereas stable overexpression of NbGPAT6a-GFP rendered leaves more resistant to infection. A loss-of-function mutation of the orthologous gene in tomato (Solanum lycopersicum), SlGPAT6, similarly resulted in increased susceptibility of leaves to Phytophthora infection concomitant with altered intracellular infection structure morphology. Conversely, Botrytis cinerea disease symptoms were reduced. Modulation of GPAT6 expression predominantly altered the outer cell wall of leaf epidermal cells. The impaired cell wall-cuticle continuum of tomato gpat6-a mutants resulted in increased water loss and these plants had fewer stomata. Our work highlights a hitherto unknown role for GPAT6-generated cutin monomers in controlling epidermal cell properties that are integral to leaf-microbe interactions and limit dehydration.

plant biology↗