Abstract
Alternaria causes pathogenic disease on various economically important crops having saprophytic to endophytic lifecycle. Pathogenic fungi of Alternaria species produce many primary and secondary metabolites (SMs). Alternaria species produce more than 70 mycotoxins. Several species of Alternaria produce various phytotoxins that are host-specific (HSTs) and non-host-specific (nHSTs). These toxins have various negative impacts on cell organelles including chloroplast, mitochondria, plasma membrane, nucleus, Golgi bodies, etc. Non-host-specific toxins such as tentoxin (TEN), Alternaric acid, alternariol (AOH), alternariol 9-monomethyl ether (AME), brefeldin A (dehydro-), Alternuene (ALT), Altertoxin-I, Altertoxin-II, Altertoxin-III, zinniol, tenuazonic acid (TeA), curvularin and alterotoxin (ATX) I, II, III are known toxins produced by Alternaria species. In other hand, Alternaria species produce numerous HSTs such as AK-, AF-, ACT-, AM-, AAL- and ACR-toxin, maculosin, destruxin A, B, etc. are host-specific and classified into different family groups. These mycotoxins are low molecular weight secondary metabolites with various chemical structures. All the HSTs have different mode of actions, biochemical reactions, and signaling mechanisms to causes diseases in the host plants. These HSTs have devastating effects on host plant tissues by affecting biochemical and genetic modifications. Host-specific mycotoxins such as AK-toxin, AF-toxin, and AC-toxin have the devastating effect on plants which causes DNA breakage, cytotoxic, apoptotic cell death, interrupting plant physiology by mitochondrial oxidative phosphorylation and affect membrane permeability. This article will elucidate an understanding of the disease mechanism caused by several Alternaria HSTs on host plants and also the pathways of the toxins and how they caused disease in plants.
Highlights
The genus Alternaria is ubiqutenious in nature, imperfecti fungi that belong to the phylum Ascomycetes of the Hyphomycetes [1,2]
alternata f. sp. lycopersici toxins (AALs)-toxin disrupting sphingolipid metabolism which promotes programmed cell death in tomato leaves promoted by ethylene and jasmonic acid and Asc gene is responsible for sphingolipid biosynthesis [82]
According to Zhang et al [82], jasmonic acid and ethylene-dependent pathways triggered by programmed cell death by AAL-toxin via sphingolipid metabolism disruption in the tomato plant, whereas according to Akamatsu et al [83] AAL-toxin lacking restriction enzyme-mediated integration (REMI) mutants are non-pathogenic in the tomato delicate plants
Summary
The genus Alternaria is ubiqutenious in nature, imperfecti fungi that belong to the phylum Ascomycetes of the Hyphomycetes [1,2]. In spite of the fact that Alternaria toxins can originate in almost entirely food and feed products and that they have the potency to exhibit harmful effects on human and animal health [35]. It is well-known that species in the Alternaria are versatile pathogens contaminating various crop plants, post-harvest fruits, refrigerated food products, as well as affecting different developmental stages of plants. We review the most important Alternaria mycotoxins, their target sites in plant organelles, and the harmful effects of these toxins cause diseases on plants
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