Dual role of Pectin Methyl Esterase activity in the regulation of plant cell wall biophysical properties

Marçal Gallemí^1,2*Juan Carlos Montesinos³Nikola Zarevski²Jan Pribyl⁴Petr Skládal⁴ClaudeEdouard Hannezo²Eva Benkova^2*

• ¹Institut Químic de Sarrià, Barcelona, Spain
• ²Institute of Science and Technology Austria (IST Austria), Klosterneuburg, Lower Austria, Austria
• ³Departamento de Bioquímica y Biología Molecular, Facultad de Farmacia, Universidad de Valencia, Spain, Burjasot, Valencia, Spain
• ⁴Centre for Molecular Medicine, Central European Institute of Technology, Masaryk University, Brno, Olomouc, Czechia

Acid-growth theory has been postulated in the 70s to explain the rapid elongation of cells in response to plant hormone auxin. More recently, it has been demonstrated that activation of the proton ATPs pump (H + -ATPs) promoting acidification of the apoplast is the principal mechanism through which hormones like auxin as well as brassinosteroids (BR) induce cell elongation. However, the impact of this acidification on the mechanical properties of the cell wall remained largely unexplored. Here, we use elongation assays and Atomic Force Microscopy (AFM) to demonstrate that acidification of apoplast is necessary and sufficient to induce cell elongation through cell wall softening. Moreover, we demonstrate that Pectin Methyl Esterase (PME) can induce both cell wall softening or stiffening in extracellular calcium dependent-manner and that tight control of PME activity is required for hypocotyl elongation.