Unraveling the Host-Selective Toxic Interaction of Cassiicolin with Lipid Membranes and Its Cytotoxicity

Abstract

Cassiicolin (Cas), a toxin produced by Corynespora cassiicola, is responsible for corynespora leaf fall disease in susceptible rubber trees. Currently, the molecular mechanisms of the cytotoxicity of Cas and its host selectivity have not been fully elucidated. Here, we analyzed the binding of Cas1 and Cas2 to membranes consisting of different plant lipids and their membrane-disruption activities. Using high-speed atomic force microscopy and confocal microscopy, we reveal that the binding and disruption activities of Cas1 and Cas2 on lipid membranes are strongly dependent on the specific plant lipids. The negative phospholipids, glycerolipids, and sterols are more sensitive to membrane damage caused by Cas1 and Cas2 than neutral phospholipids and betaine lipids. The mature Cas1 and Cas2 play an essential role in causing membrane disruption. Cytotoxicity tests on rubber leaves of RRIV 1, RRIV 4, and PB 255 clones suggest that the toxins cause necrosis of rubber leaves, except for the strong resistance of PB 255 against Cas2. Cryo-SEM analyses of necrotic leaf tissues treated with Cas1 confirm that cytoplasmic membranes are vulnerable to the toxin. Thus, the host selectivity of Cas toxin is attained by the lipid-dependent binding activity of Cas to the membrane, and the cytotoxicity of Cas arises from its ability to form biofilm-like structures and to disrupt specific membranes.

The Necrosis- and Ethylene-inducing peptide 1-like protein (NLP) gene family of the plant pathogen Corynespora cassiicola

“…Levels of host specialization suggest the involvement of specialized effectors that are recognized by a limited range of compatible hosts (Lopez et al 2018; Gao et al 2020). So far, the necrotrophic toxin cassiicolin is the only completely characterized effector of C. cassiicola (Breton et al 2000; de Lamotte et al 2007; Déon et al 2014; Lopez et al 2018; Ngo et al 2022). Cassiicolin is an accessory effector, which means it is lineage specific and may not occur in all C. cassiicola isolates (Déon et al 2014; Lopez et al 2018; Wu et al 2018).…”