Serine Proteinases Secreted by Two Isolates of the Fungus Alternaria solani

Abstract

It is well-known Alternaria solani Sorauer is the causative agent of alternariosis. In this paper, serine proteinases secretion by two genetically related isolates of the fungus, collected from potato and tomato plants grown in central Russia have been studied. The data clarify functions of these enzymes in the process of pathogenesis in which they can play a pivotal role. Also, the data should allow classifying Alternaria’s strains more precisely. It was found that the two isolates produced trypsin-like and subtilisin-like proteinases during growth both in synthetic culture medium and in medium containing heat-stable vegetable proteins. There were significant differences in the influence of the environment on the serine proteinase secretion by the potato and tomato isolates of A. solani. The proportion of such serine proteinases as trypsin-like and subtilisin-like enzymes depends on the composition of the growth medium, especially on the available organic nitrogen form, as well as features both of the pathogenic fungus and of the host plant. So, the tomato isolate demonstrated weak growth and low level or absence of serine proteinase excretion on cultivation with the medium containing proteins extracted from potato tubers and pea seeds. The potato isolate secreted many more serine proteinases, among which the trypsin-like enzymes dominated. Our data suggest that the tomato isolate, when grown on medium with proteins extracted from potato tubers, lost pathogenicity and became to behave as a saprophyte, while the potato isolate retained its pathogenic properties on growth on any tested medium.

Serine Exoproteinases Secreted by the Pathogenic Fungi of Alternaria Genus

“…The previous data [11] indicate the absence of the clear correlation of the serine exoproteases composition with the nature of host plants.…”

“…Simultaneously, such medium would be a model for studying the infection process. It was also demonstrated that during Alternaria growth in this medium, fungi produced extracellular proteinases with the slightly alkaline activity optimum [11]. Figure 1 shows the results of the study of proteinases excretion by the mentioned 13 isolates.…”

“…As we have shown previously [11], the phytopathogenic Alternaria fungi can be grown in the medium containing thermostable proteins of pea and carrot, because the combination of these plant components provides the optimum mycelium growth level of the isolates under study. Simultaneously, such medium would be a model for studying the infection process.…”

“…The fungi maintenance and their growing as a submersed culture in the liquid medium (pea-carrot broth) were carried out as described earlier [11]. After 2, 5, 7, 10, 14, and 18 days of the growth, the mycelium was harvested on a weighed Whatman No.…”

“…In Alternaria spp. the proteases excretion has been shown and it is considered that these enzymes may function as pathogenic factors in some fungus-plant interactions [10,11]. It has been also suggested that proteases can facilitate the local penetration of a plant cell wall by breaking down the fibrous glycoproteins that contribute to its stability [12].…”