Plant triterpenoid saponins function as susceptibility factors to promote the pathogenicity of Botrytis cinerea

The gray mold fungus Botrytis cinerea is a necrotrophic pathogen that causes diseases in hundreds of plant species,including high-value crops.Its polyxenous nature and pathogenic success are due to its ability to perceive host signals in its favor.In this study,we found that laticifer cells of Euphorbia lathyris are a source of susceptibility factors required by B.cinerea to cause disease.Consequently,poor-in-latex(pil)mutants,which lack laticifer cells,show full resistance to this pathogen,whereas lot-of-latex mutants,which produce more laticifer cells,are hypersusceptible.These S factors are triterpenoid saponins,which are widely distributed natural products of vast structural diversity.The downregulation of laticifer-specific oxydosqualene cyclase genes,which encode the first committed step enzymes for triterpene and,therefore,saponin biosynthesis,conferred disease resistance to B.cinerea.Likewise,the Medicago truncatula Iha-1 mutant,compromised in triterpenoid saponin biosynthesis,showed enhanced resistance.Interestingly,the application of different purified triterpenoid saponins pharmacologically complemented the diseaseresistant phenotype ofpil and hla-1 mutants and enhanced disease susceptibility in different plant species.We found that triterpenoid saponins function as plant cues that signal transcriptional reprogramming in B.cinerea,leading to a change in its growth habit and infection strategy,culminating in the abundant formation of infection cushions,the multicellular appressoria apparatus dedicated to plant penetration and biomass destruction in B.cinerea.Taken together,these results provide an explanation for how plant triterpenoid saponins function as disease susceptibility factors to promote B.cinerea pathogenicity.

Inhibition of Botrytis cinerea and control of gray mold on table grapes by calcium propionate

Objectives:The gray mold fungus Botrytis cinerea(B.cinerea)infects a wide range of crops before and after harvest,causing huge losses worldwide.Inhibition mechanisms of B.cinerea in vitro and in plants by calcium propionate(CP),generally recognized as a safe substanee,are described in this study.Materials and methods:Wild-type and transgenic mutant strains of B.cinerea were used in the study to evaluate the effects of CP on fun gal growth and developme nt in vitro.Plant materials in cludi ng tomato leaves and table grapes were tested for con trolling efficie ncy of CP agai nst gray mold deterioration in vivo.Results:Mycelial growth of B.cinerea was inhibited by CP in a dose-dependent manner with occasional disruption of hyphal tips,causing cellular collapse and efflux of cell contents.Staining with fluorescein diacetate and propidium iodide indicated that CP decreased fungal cell viability.Inhibition efficiency of CP against B.cinerea was enhaneed by reducing pH.In contrast,the veil mutant,which exhibited deficiency in acid production,was more resista nt to CP,suggesti ng that inhibition of B.cinerea by CP is enhanced by the acidification ability of the fungus itself.Additionally,CP inhibited infection cushion development by germlings of B.cinerea.Infection assays with tomato leaves and table grapes showed that CP inhibited decay development in both host tissues.Moreover,application of CP on grapes 3 days prior to harvest could contribute to management of deterioration caused by spontaneous fungal diseases during storage.Conclusion:CP can suppress hyphal growth,inhibit infection cushion development,and reduce the virulence of B.cinerea.CP is thus promising for practical management of gray mold in fruit crops and merits further evaluation.