Callose-mediated resistance to pathogenic intruders in plant defense-related papillae

Abstract

Plants are exposed to a wide range of potential pathogens, which derive from diverse phyla. Therefore, plants have developed successful defense mechanisms during co-evolution with different pathogens. Besides many specialized defense mechanisms, the plant cell wall represents a first line of defense. It is actively reinforced through the deposition of cell wall appositions, so-called papillae, at sites of interaction with intruding microbial pathogens. The papilla is a complex structure that is formed between the plasma membrane and the inside of the plant cell wall. Even though the specific biochemical composition of papillae can vary between different plant species, some classes of compounds are commonly found which include phenolics, reactive oxygen species, cell wall proteins, and cell wall polymers. Among these polymers, the (1,3)-β-glucan callose is one of the most abundant and ubiquitous components. Whereas the function of most compounds could be directly linked with cell wall reinforcement or an anti-microbial effect, the role of callose has remained unclear. An evaluation of recent studies revealed that the timing of the different papilla-forming transport processes is a key factor for successful plant defense.

Cellulose and callose synthesis and organization in focus, what's new?

“…Combined use of the dye S4B [53] and the callose-specific dye aniline blue fluorochrome (ABF) [64**,78] facilitated three-dimensional, nanoscale cell wall images that revealed a direct interaction of cellulose and callose microfibrils within the area of forming callosic papillae, induced by pathogenic powdery mildew in Arabidopsis leaves [79**]. These results suggest a permeation of callose fibrils through internal cell wall nanopores, which would require a gel-like condition of callose that may be pH dependent [80]. Overexpression of GSL5 enhanced callose deposition at these interaction sites [64**] and expanded the cellulose/callose network, and led to formation of a callose layer on top of the pre-existing cellulosic cell wall structure [79**,80].…”

Plant cell wall in pathogenesis, parasitism and symbiosis

“…The review by Delaunois and co-worker provides an insight into the modulation of the apoplastic protein patterns during pathogen infection (Delaunois et al, 2014). Super-resolution microscopy using microscopy combined with specific and efficient labeling techniques yield information on three-dimensional modifications of cell wall polymers (i.e., callose-cellulose network) at the site of attempted microbial penetration (Voigt, 2014). Carbohydrate microarrays, combining the specificity of monoclonal antibodies and carbohydrate binding modules with the multiplexed analysis capacity of microarrays, represent a promising technique to study the changes in cell wall micro-domains during plant/biotic interaction (Malinovsky et al, 2014).…”

“…At sites of interaction with intruding microbial pathogens the cell wall is actively reinforced through the deposition of cell wall appositions, so-called papillae. Voigt present a perspective article that discusses the possible roles of the (1,3)-β-glucan callose and the other papillae components in plant defense (Voigt, 2014). Lignin is both pathogen-induced and developmentally deposited in the secondary thickened cell wall.…”

Quantification of stimulus-induced callose spots on plant materials

“…Well known example is the accumulation of callose as a major component of papillae, which is an apposition of a specialized cell wall at the site of attempted penetration of fungal or oomycete pathogens and plays an important role as the first line of defense (Collinge 2009;Underwood and Somerville 2008;Voigt 2014). Hence, the accumulation of callose has been used as an index of defense responses induced by pathogen infection and elicitor treatment.…”

“…Plants are known to synthesize and accumulate callose, a β-1,3-linked glucan, in response to pathogen infection, elicitor treatment and wounding (Chen and Kim 2009;Voigt 2014). Well known example is the accumulation of callose as a major component of papillae, which is an apposition of a specialized cell wall at the site of attempted penetration of fungal or oomycete pathogens and plays an important role as the first line of defense (Collinge 2009;Underwood and Somerville 2008;Voigt 2014).…”