Colletotrichum acutatum interactions with unripe and ripe strawberry fruits and differential responses at histological and transcriptional levels

Abstract

Microscopic investigations were conducted into the interaction of Colletotrichum acutatum on white and red strawberry (Fragaria ·ananassa) fruit surfaces. The results showed that, whilst the early interaction events were similar in both white and red fruits, after 24 h fungal colonization dramatically varied: in white fruits C. acutatum became quiescent as melanized appressoria, but on red fruits it displayed subcuticular necrotrophic invasion. A microarray analysis of white and red strawberries after 24 h of interaction with C. acutatum was performed, in order to reveal differences in gene expression possibly related to the different susceptibility of unripe and ripe fruits. Epi ⁄ catechin-related genes and fatty acid metabolism genes, involved in the production of quiescence-related molecules such as flavan-3-ols, proanthocyanidins and antifungal dienes, were found to be regulated during strawberry ripening, supporting a role for these molecules as preformed defence mechanisms. Besides several genes commonly regulated upon pathogen interaction, different genes were specifically transcribed only in white or red challenged fruits; a number of these, such as those coding for lectin and polyphenol oxidase, possibly account for specific pathogen-induced responses. The putative biological role of these genes in the different susceptibility of fruits to C. acutatum is discussed.

Unfoldome variation upon plant-pathogen interactions: strawberry infection by Colletotrichum acutatum

“…In the present analysis, we transposed the DEGs found by the above microarray analysis onto the F. vesca diploid genome, whose sequence is available (Shulaev et al 2011), to overcome ambiguities associated with the octaploid genome configuration of F. x ananassa (Guidarelli et al 2011). In the original microarray analysis, 50,456 oligoprobes derived from the TIGR Plant Transcript Assemblies database (http://plantta.jcvi.org/) were analyzed: 78.1 % (39,421) derived from F. vesca, 21.1 % (10,669) from F. x ananassa, and 0.7 % (366) from Malus domestica (Guidarelli et al 2011).…”

“…Subsequently, it switches to necrotrophic colonization, killing the host tissue to extract nutrients from the dead host cells (Guidarelli et al 2011). Previous microarray experiments highlighted the genes differentially expressed in F. x ananassa strawberry white or red fruit upon C. acutatum infection (Guidarelli et al 2011). In this analysis, four conditions were considered, involving genes expressed in unripe white (W) fruits and in ripe red (R) fruits, both inoculated with water (H) or with the fungus (I).…”

“…Symptoms of fungal infection become visible after five or six days from artificial inoculation in ripe fruits, in which the pathogen quickly penetrates and invades internal tissues (Guidarelli et al 2011). Conversely, upon interaction with unripe fruit, the pathogen stops its growth shortly after spore germination (24 h) and becomes quiescent before penetration as melanized appressorium (Guidarelli et al 2011).…”

“…Symptoms of fungal infection become visible after five or six days from artificial inoculation in ripe fruits, in which the pathogen quickly penetrates and invades internal tissues (Guidarelli et al 2011). Conversely, upon interaction with unripe fruit, the pathogen stops its growth shortly after spore germination (24 h) and becomes quiescent before penetration as melanized appressorium (Guidarelli et al 2011). Previously, a wide microarray analysis of transcriptome variation in the differentially susceptible unripe and ripe strawberry (Fragaria x ananassa) fruits upon infection with C. acutatum has been performed (Guidarelli et al 2011).…”

“…Conversely, upon interaction with unripe fruit, the pathogen stops its growth shortly after spore germination (24 h) and becomes quiescent before penetration as melanized appressorium (Guidarelli et al 2011). Previously, a wide microarray analysis of transcriptome variation in the differentially susceptible unripe and ripe strawberry (Fragaria x ananassa) fruits upon infection with C. acutatum has been performed (Guidarelli et al 2011). The study reported the difference in gene expression in white unripe and red ripe strawberry fruits, both in the absence and in the presence of pathogen inoculation.…”