Alternaria Toxins: Potential Virulence Factors and Genes Related to Pathogenesis

Abstract

Alternaria is an important fungus to study due to their different life style from saprophytes to endophytes and a very successful fungal pathogen that causes diseases to a number of economically important crops. Alternaria species have been well-characterized for the production of different host-specific toxins (HSTs) and non-host specific toxins (nHSTs) which depend upon their physiological and morphological stages. The pathogenicity of Alternaria species depends on host susceptibility or resistance as well as quantitative production of HSTs and nHSTs. These toxins are chemically low molecular weight secondary metabolites (SMs). The effects of toxins are mainly on different parts of cells like mitochondria, chloroplast, plasma membrane, Golgi complex, nucleus, etc. Alternaria species produce several nHSTs such as brefeldin A, tenuazonic acid, tentoxin, and zinniol. HSTs that act in very low concentrations affect only certain plant varieties or genotype and play a role in determining the host range of specificity of plant pathogens. The commonly known HSTs are AAL-, AK-, AM-, AF-, ACR-, and ACT-toxins which are named by their host specificity and these toxins are classified into different family groups. The HSTs are differentiated on the basis of bio-statistical and other molecular analyses. All these toxins have different mode of action, biochemical reactions and signaling mechanisms to cause diseases. Different species of Alternaria produced toxins which reveal its biochemical and genetic effects on itself as well as on its host cells tissues. The genes responsible for the production of HSTs are found on the conditionally dispensable chromosomes (CDCs) which have been well characterized. Different bio-statistical methods like basic local alignment search tool (BLAST) data analysis used for the annotation of gene prediction, pathogenicity-related genes may provide surprising knowledge in present and future.

Pantoea ananatisdefeatsAlliumchemical defenses with a plasmid-borne virulence gene cluster

“…The pathogenic lifestyle of P. ananatis on onion more closely resembles that of some necrotrophic plant pathogenic fungi such as Alternaria or Fusarium than other described bacterial plant pathogens. These fungal pathogens produce phytotoxins as important virulence factors and proliferate on dead plant tissue (42, 43). In the case of Fusarium oxysporum f. sp.…”

The distribution of mycotoxins in a heterogeneous wheat field in relation to microclimate, fungal and bacterial abundance

“…The clarification of the metabolic pathways leading to mycotoxin production is therefore needed to develop genetic markers able to target the genes involved in mycotoxin production (Meena et al . ).…”

“…From endophytes, to saprophytes to pathogens, the interactions of Alternaria with their hosts is various (Thomma ; Meena et al . ). The presence of Alternaria is often associated with cereal fungal diseases such as the black head moulds (or black point) of wheat and barley and the Alternaria leaf blight disease (Culshaw et al .…”

“…; Meena et al . ). Alternaria mycotoxins are found across the whole food chain and in a large number of food commodities, due to the ubiquitous nature of this genus.…”

Tools of the crook‐ infection strategies of fungal plant pathogens

“…Similarly, PMtoxin-deficient Tox À mutants of M. zeae-maydis lost the ability to infect Tcms maize (Yun et al, 1998). Besides mitochondria, HSTs are also reported to target enzymes or other plant cell organelles like plasma membrane, chloroplast, endoplasmatic reticulum, nucleus, vacuole and Golgi bodies, with the objective to suppress host defence responses and/or induce host cell death (Meena et al, 2017).…”