Abstract
Fungal plant pathogens are major threats to food security worldwide. Sclerotinia sclerotiorum and Botrytis cinerea are closely related Ascomycete plant pathogens causing mold diseases on hundreds of plant species. There is no genetic source of complete plant resistance to these broad host range pathogens known to date. Instead, natural plant populations show a continuum of resistance levels controlled by multiple genes, a phenotype designated as quantitative disease resistance. Little is known about the molecular mechanisms controlling the interaction between plants and S. sclerotiorum and B. cinerea but significant advances were made on this topic in the last years. This minireview highlights a selection of nine themes that emerged in recent research reports on the molecular bases of plant-S. sclerotiorum and plant-B. cinerea interactions. On the fungal side, this includes progress on understanding the role of oxalic acid, on the study of fungal small secreted proteins. Next, we discuss the exchanges of small RNA between organisms and the control of cell death in plant and fungi during pathogenic interactions. Finally on the plant side, we highlight defense priming by mechanical signals, the characterization of plant Receptor-like proteins and the hormone abscisic acid in the response to B. cinerea and S. sclerotiorum, the role of plant general transcription machinery and plant small bioactive peptides. These represent nine trends we selected as remarkable in our understanding of fungal molecules causing disease and plant mechanisms associated with disease resistance to two devastating broad host range fungi.
Highlights
A majority of studies on plant interactions with fungal pathogens over the last years have focused on specialized host–pathogen interactions
In Arabidopsis acd5 mutant, ceramides were associated with autophagy and enhanced susceptibility to B. cinerea, but these two activities may be independent (Bi et al, 2014; Magnin-Robert et al, 2015). These findings indicate that certain mechanisms of host cell death may be favorable to necrotrophic fungi whereas others would be detrimental (Dickman and de Figueiredo, 2013)
Small bioactive peptides are defined as proteins of about 100 amino acids with roles in plant development, reproduction or interaction with the environment (Tavormina et al, 2015)
Summary
A majority of studies on plant interactions with fungal pathogens over the last years have focused on specialized host–pathogen interactions. How these broad host range fungal pathogens cause disease and what are the genetic bases of plant QDR is still poorly understood. Secondary metabolite toxins and cell wall-degrading enzymes are known to contribute to virulence of necrotrophic fungi (Choquer et al, 2007; Kabbage et al, 2015), but knowledge on the repertoires and mode of action of S. sclerotiorum and B. cinerea proteins secreted during host colonization remains limited.
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