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.

Highlights

  • Fungal kingdom is very interesting in both useful and harmful point of view, which includes more than 1.5 million species, but only 100,000 species have been described, out of them 15,000 species cause disease in plants (Maharshi and Thaker, 2012)

  • restriction mediatedintegration transformation (REMI) techniques used for AKT protein and AKT1 gene tagging to mutagenize which is required for biosynthesis of AK-toxin and pathogenicity of the Japanese pear pathotype (Tanaka et al, 1999; Wolpert et al, 2002)

  • Genomic and transcriptomic comparisons are taken in use to obtain genetic features of fungal pathogen to survive successfully in various stressful ecological habitats and to survive itself in different pathogenic life styles

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Summary

Introduction

Fungal kingdom is very interesting in both useful and harmful point of view, which includes more than 1.5 million species, but only 100,000 species have been described, out of them 15,000 species cause disease in plants (Maharshi and Thaker, 2012). DNADNA analysis has suggested a close relationship between HSTs producing Alternaria fungal species and non-pathogenic A. alternata (Kuninaga and Yokozawa, 1987). Another HSTs is HC-toxin (a cyclic tetrapeptide), a well-known produced toxin by the plant pathogenic fungus Cochliobolus carbonum, has been discovered in the species of Alternaria jesenskae, pathotype of Fumana procumbens, and the gene responsible for this toxin is AjTox2 identified by genomic sequencing.

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