Host-selective toxins produced by the plant pathogenic fungusAlternaria alternata

Abstract

Host-selective toxins (HSTs) produced by fungal plant pathogens are generally low-molecular-weight secondary metabolites with a diverse range of structures that function as effectors controlling pathogenicity or virulence in certain plant-pathogen interactions. There are now seven known diseases caused by Alternaria alternata in which HSTs are responsible for fungal pathogenesis. The pathogens have been defined as pathotypes of A. alternata because of morphological similarity but pathological differences. Chemical structures of HSTs from six pathotypes have been determined. The role of A. alternata HSTs in pathogenesis has been studied extensively, and discovery of the release of HSTs from germinating conidia prior to penetration aids in understanding the early participation of HSTs to induce susceptibility of host cells by suppressing their defence reactions. Many attempts have been made to find the target sites of A. alternata HSTs, and four cellular components, plasma membrane, mitochondrion, chloroplast and a metabolically important enzyme, have been identified as the primary sites of each HST action, leading to elucidation of the molecular mechanisms of HST sensitivity in host plants. Studies of the molecular genetics of HST production have identified supernumerary chromosomes encoding HST gene clusters and have provided new insights into the evolution of A. alternata pathotypes.

Alternaria alternata transcription factor CmrA controls melanization and spore development

“…Al. alternata causes large economic losses of food and feed every year, because it not only produces melanin but a large variety of secondary metabolites such as carcinogenic alternariol (Pruß et al, 2014;Saha et al, 2012;Tsuge et al, 2013). As in other organisms, it was shown that melanin-deficient strains are more sensitive to UV light (Kawamura et al, 1999).…”

Natural Dibenzo-α-Pyrones and Their Bioactivities

“…The metabolites from fungal pathogens are usually toxic to plants and are called phytotoxins which are divided into host-specific [83,84] and host non-specific toxins [85,86]. Some Alternaria-derived dibenzo-α-pyrones were approved as the host-specific phytotoxins including altenuene (1), alternariol (10), alternariol 9-methyl ether (11), alternuisol (15), and dehydroaltenusin (17) [9,10,37,39,41,45].…”

Assessing the Genetic Diversity of <i>Alternaria Bataticola</i> in South Africa using Molecular Markers

“…Significant levels of diversity in Alternaria species have also been reported using other molecular techniques such as microsatellites [34] and amplified fragment length polymorphism markers (AFLP) [35]. In addition to this, high levels of variation in Alternaria species have also been observed using other techniques like morphometric characters [36], structures of host-selective toxins (HSTs) [37] and protein analysis [38]. The isolates from the three sweetpotato cultivars (Excel, Beauregard and W-119) grouped together with some breeding lines in the subclusters of cluster I. Excel, Beauregard and W-119 originated from the USA and are used in the sweetpotato breeding programme at ARC-VOPI.…”