Abstract
Plants are constantly exposed to a wide range of potential pathogens and to protect themselves, have developed a variety of chemical and physical defense mechanisms. Callose is a β-(1,3)-D-glucan that is widely distributed in higher plants. In addition to its role in normal growth and development, callose plays an important role in plant defense. Callose is deposited between the plasma membrane and the cell wall at the site of pathogen attack, at the plasmodesmata, and on other plant tissues to slow pathogen invasion and spread. Since it was first reported more than a century ago, defense-related callose deposition has been extensively studied in a wide-spectrum of plant-pathogen systems. Over the past 20 years or so, a large number of studies have been published that address the dynamic nature of pathogen-induced callose deposition, the complex regulation of synthesis and transport of defense-related callose and associated callose synthases, and its important roles in plant defense responses. In this review, we summarize our current understanding of the regulation and function of defense-related callose deposition in plants and discuss both the progresses and future challenges in addressing this complex defense mechanism as a critical component of a plant immune system.
Highlights
We have recently shown that two Arabidopsis homologs of UBAC2, a conserved endoplasmic reticulum (ER) protein implicated in ER quality control and ER-associated degradation (ERAD), play a critical role in pathogen- and pathogen-associated molecular patterns (PAMPs)-induced callose deposition [39]
Callose as the most prominent cell wall component of papillae was first reported more than 120 years ago and has received extensive attention in the research on the physical and chemical basis of plant disease resistance
There are still many important questions remained to be addressed in order to fully understand the roles of defense-related callose deposition in plant immune responses
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Callose is present in sieve plates, a basic component of the phloem, under normal growing and developmental conditions and can accumulate rapidly and plugs the sieve pores when subjected to stress [5,6] Similar to this stress response, callose biosynthesis and degradation in the neck region of plasmodesmata help to regulate permeability during abiotic and biotic stresses [7]. Callose is deposited between the plasma membrane and the pre-existing cell wall at sites of pathogen attack [8] This pathogen-induced callose deposition functions as a chemical and physical defense mechanism for reinforcing plant cell wall and plays an essential role in the defense response to invading pathogens. We summarize these progresses in our understanding of the defense-related callose deposition in plants and discuss both the significance and future challenges of unraveling this complex defense mechanism as a critical component of the plant immune system
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