Callose metabolism and the regulation of cell walls and plasmodesmata during plant mutualistic and pathogenic interactions

Abstract

Cell walls are essential for plant growth and development, providing support and protection from external environments. Callose is a glucan that accumulates in specialized cell wall microdomains including around intercellular pores called plasmodesmata. Despite representing a small percentage of the cell wall (~0.3% in the model plant Arabidopsis thaliana), callose accumulation regulates important biological processes such as phloem and pollen development, cell division, organ formation, responses to pathogenic invasion and to changes in nutrients and toxic metals in the soil. Callose accumulation modifies cell wall properties and restricts plasmodesmata aperture, affecting the transport of signaling proteins and RNA molecules that regulate plant developmental and environmental responses. Although the importance of callose, at and outside plasmodesmata cell walls, is widely recognized, the underlying mechanisms controlling changes in its synthesis and degradation are still unresolved. In this review, we explore the most recent literature addressing callose metabolism with a focus on the molecular factors affecting callose accumulation in response to mutualistic symbionts and pathogenic elicitors. We discuss commonalities in the signaling pathways, identify research gaps and highlight opportunities to target callose in the improvement of plant responses to beneficial versus pathogenic microbes.

NONEXPRESSOR OF PATHOGENESIS-RELATED GENEScontrol Huanglongbing tolerance by regulating immune balance in citrus plants

“…However, overaccumulation of callose can cause phloem plugging, contributing to HLB symptom development. It is well known that callose levels are determined by the equilibrium between synthesis and removal 59 . For instance, SA treatment and pathogen infection in Arabidopsis simultaneously induce the expression of callose biosynthetic genes including AtCalS1 and AtCalS12 as well as catabolic genes such as PR2 that encodes a β-1,3-glucanase degrading callose 60 .…”

A viral protein activates MAPKs pathway to promote viral infection by downregulating callose deposition in plants

“…Moreover, callose deposition near the neck zone of plasmodesmata regulates their size exclusion limit (SEL), which is responsible for the cell-to-cell transport of small and large molecules, including RNAs and transcription factors (TFs) 49 . The REMORIN (REM) family is one of the best-characterized PM nanodomain-associated proteins in plants [50][51] . Studies on different Arabidopsis remorin proteins have demonstrated their segregation into distinct membrane microdomains on individual cell surfaces, directly involving in callose biosynthesis 52 .…”

Evolutionary history of the main extracellular matrix polysaccharides in brown algae

“…ischiensis [19,86]. Plasmodesmata have been shown to be crucial in cell-to-cell signaling in land plants and may play a role in the evolution of tissue complexity [87][88][89]. Thus, it is not only the building up of a consistent and dynamic glycan-rich ECM in brown algae that may have contributed to the evolution of complex multicellular organisms, but also some structural features that function in close vicinity to ECMs such as plasmodesmata.…”