Plant beta-1, 3-glucanases are pathogenesis-related proteins, which are implicated in plant defense responses against pathogen infection. As an initial step in understanding the roles of beta-1, 3-glucanases in the strawberry plant defense system, genome walking, and 3' and 5' RACE were performed to isolate beta-1, 3-glucanase genomic and cDNA clones. In addition, real time PCR was performed to determine the expression levels of two of the isolated beta-1, 3-glucanase genes in healthy and fungal infected plants.
Two genomic clones, FaBG2-1 and FaBG2-2, and a cDNA clone, FaBG2-3, encoding three different beta-1, 3-glucanases, were isolated. FaBG2-1 was comprised of two exons and one intron. The first exon of FaBG2-1 encodes the major part of a signal peptide. Results of Southern blotting analysis indicated that the strawberry genome contains several copies of FaBG2-1 or related genes. FaBG2-2 appears to be an intronless gene and does not encode a signal peptide. FaBG2-3, like FaBG2-1, also encodes a signal peptide, but is different from FaBG2-1 in 3' and 5' non-coding regions. The proteins encoded by these three genes share a high degree of sequence homology to plant class II beta-1, 3-glucanases.
The expression of FaBG2-1 and FaBG2-3 in strawberry plants infected with Colletotrichum fragariae and Colletotrichum acutatum, two important strawberry fungal pathogens, were examined. High levels of induction of both genes were observed in plants infected with C. fragariae, whereas lower levels of induction were observed in plants infected with C. acutatum. Moreover, the expression of FaBG2-3 was much greater than FaBG2-1 in both the uninfected and the infected plants.
The expressions of FaBG2-1 and FaBG2-3 in leaves, crowns, and roots were examined at different time points during a 7 month growth period. Different organs showed different expression patterns for the two genes. Furthermore, the total beta-1, 3-glucanase activity and isozyme pattern were analyzed. The isozyme patterns were different between the uninfected and the infected plants. Also, the differences were observed between young plants and older plants. This research shows that beta-1, 3-glucanase in strawberry plant may play roles in plant defense and plant development.