Immunolocalization and functional role of Sclerotium rolfsii lectin in development of fungus by interaction with its endogenous receptor

Abstract

Many fungi are known to secrete lectins, but their functional roles are not clearly understood. Sclerotium rolfsii, a soilborne plant pathogenic fungus capable of forming fruiting bodies called sclerotial bodies, secrete a cell wall-associated Thomsen-Friedenreich antigen-specific lectin. To understand the functional role of this lectin, we examined its occurrence and expression during development of the fungus. Furthermore, putative endogenous receptors of the lectin were examined to substantiate the functional role of the lectin. Immunolocalization studies using FITC-labeled lectin antibodies revealed discrete distribution of lectin sites at the branching points of the developing mycelia and uniformly occurring lectin sites on the mature sclerotial bodies. During development of the fungus the lectin is expressed in small amounts on the vegetative mycelia and reaching very high levels in mature sclerotial bodies with a sudden spurt in secretion at the maturation stage. Capping of the lectin sites on the sclerotial bodies by lectin antibodies or haptens inhibit strongly the germination of these bodies, indicating functional significance of the lectin. At the maturation stage the lectin interacts with the cell wall-associated putative endogenous receptor leading to the aggregation of mycelium to form sclerotial bodies. The lectin-receptor complex probably acts as signaling molecule in the germination process of sclerotial bodies. Using biotinylated lectin, the receptors were identified by determining the specific lectin binding to lipid components, extracted from sclerotial bodies, and separated on thin-layer chromatograms. Preliminary characterization studies indicated that the receptors are glycosphingolipids and resemble inositolphosphoceramides. These findings together demonstrate the importance of lectin-receptor interactions to explain hitherto speculated functional role of the lectins and also the glycosphingolipids of fungi.

Entomotoxic and nematotoxic lectins and protease inhibitors from fungal fruiting bodies

“…In accordance with this, the expression of TAP1 was demonstrated to be strongly upregulated during fruiting body formation (Nowrousian and Cebula 2005). Similarly, expression of SRL is much higher in sclerotia than in vegetative mycelium (Swamy et al 2004). Using respective knockout mutants, TAP1 and AOL 2 were shown not to be essential for the formation of fruiting bodies (Nowrousian and Cebula 2005) or the function of nematode traps, respectively (Balogh et al 2003).…”

“…In fungi, lectins have been implicated in defense against fungivores , in fungal developmental processes including fruiting body formation (Luan et al 2010;Swamy et al 2004;Wang et al 1998), in molecular recognition during mycorrhization or parasitism (Guillot et al 1994;Guillot and Konska 1997;Wang et al 1998), and in storage of nutrients (Kellens and Peumans 1990). Most experimental evidence is in support of the defensive function of fungal lectins, which is mediated by binding of the lectin to non-self glycans on the cells of the target organism (Künzler 2015).…”

A potent mitogenic lectin from the mycelia of a phytopathogenic fungus, Rhizoctonia bataticola, with complex sugar specificity and cytotoxic effect on human ovarian cancer cells

“…The lectin isolated from Rhizoctonia crocorum and the lectin from Agaricus blazei are both tetramers consisting of 11 kDa and 16 kDa subunits, respectively [22,23]. Similarly, a lectin isolated from Sclerotium rolfsii is a homo dimer with subunit mass of 17 kDa, which shows pH dependent oligomerization [24,25]. The N-terminal amino acid in RBL is blocked which was indicated by its failure to release dansyl derivative.…”

New lectins from aspergilli and their carbohydrate specificity

“…A. nidulans has also been reported to ex- press lectin activity after 6 days of growth (Singh et al 2010c). Developmental regulation of lectin activity has also been reported in Sclerotium rolfsii (Swamy et al 2004) and Rhizoctonia solani (Kellens & Peumans 1991). The agglutination activity from Sclerotium rolfsii has been found dependent on the age of the culture and optimal activity has been reported after 5 days of cultivation and was lost after 7 days of growth (Barak et al 1985).…”