The Role of the Primary Cell Wall in Plant Morphogenesis

Abstract

Morphogenesis remains a riddle, wrapped in a mystery, inside an enigma. It remains a formidable problem viewed from many different perspectives of morphology, genetics, and computational modelling. We propose a biochemical reductionist approach that shows how both internal and external physical forces contribute to plant morphogenesis via mechanical stress-strain transduction from the primary cell wall tethered to the plasma membrane by a specific arabinogalactan protein (AGP). The resulting stress vector with direction defined by Hechtian adhesion sites, has a magnitude of a few picoNewtons amplified by a hypothetical Hechtian growth oscillator. This paradigm shift involves stress activated plasma membrane Ca . Thus, as the immediate source of cytosolic Ca 2+ an AGP-Ca 2+ capacitor directs vectorial exocytosis of cell wall precursors and auxin efflux (PIN) proteins. In toto these components comprise the Hechtian Oscillator and also the gravisensor. Thus interdependent auxin and Ca 2+ morphogen gradients account for the predominance of AGPs. The size and location of a cell surface AGP-Ca 2+-capacitor is essential to differentiation and explains AGP correlation with all stages of morphogenetic patterning from embryogenesis to root and shoot. Finally, evolutionary origins of the Hechtian Oscillator in the unicellular Chlorophycean algae reflect the ubiquitous role of chemiosmotic proton pumps that preceded DNA at the dawn of life.

A Hybrid Approach Enabling Large-Scale Glycomic Analysis of Post-Golgi Vesicles Reveals a Transport Route for Polysaccharides

“…However, this requires further investigation, since both the glycosyltransferases and the AGP protein core are not leaderless proteins and are expected to follow canonical secretory pathways (van de Meene et al, 2017). Given that glycosylated proteins at the cell wall serve many functions, including signaling and responses to biotic and abiotic stress (Cantu et al, 2008;Chaliha et al, 2018;Lamport et al, 2018;Novakovic et al, 2018), understanding the mechanisms regulating their secretion under different stimuli is critical for determining their functions. The approach presented here provides supporting evidence for a TGN-mediated pathway for extracellular glycoproteins and an alternative means to conventional proteomics toward dissecting their delivery pathways via the endomembrane system.…”

Calcium Binding by Arabinogalactan Polysaccharides Is Important for Normal Plant Development

“…The AGP-Ca 21 capacitor model suggests that AGPs can store Ca 21 and release it in a pH-dependent manner (Lamport and Várnai, 2013;Lamport et al, 2014Lamport et al, , 2018b. Ca 21 could suggest a role for AGPs in Ca 21 buffering or homeostasis because the binding is pH dependent.…”

The role of arabinogalactan proteins (AGPs) in fruit ripening—a review

“…The mechanism of these processes is as follows: H + dissociates AGP-Ca 2+ increasing free cytosolic Ca 2+ , which is involved with the exocytosis of cell wall ingredients 25 . The existence of an AGP-Ca 2+ capacitor is crucial in AGP functions in morphogenetic patterning and embryogenesis as a primary origin of cytosolic Ca 2+ waves and, secondly, as a pectic plasticizer 20 , 25 , 26 .…”