Temporal and Spatial Profiles of Chitinase Expression by Norway Spruce in Response to Bark Colonization by Heterobasidion annosum

Abstract

Pathogen colonization and transcript levels of three host chitinases, putatively representing classes I, II, and IV, were monitored with real-time PCR after wounding and bark infection by Heterobasidion annosum in 32-year-old trees of Norway spruce (Picea abies) with low (clone 409) or high (clone 589) resistance to this pathogen. Three days after inoculation, comparable colonization levels were observed in both clones in the area immediately adjacent to inoculation. At 14 days after infection, pathogen colonization was restricted to the area immediately adjacent to the site of inoculation for clone 589 but had progressed further into the host tissue in clone 409. Transcript levels of the class II and IV chitinases increased after wounding or inoculation, but the transcript level of the class I chitinase declined after these treatments. Transcript levels of the class II and class IV chitinases were higher in areas immediately adjacent to the inoculation site in clone 589 than in similar sites in clone 409 3 days after inoculation. This difference was even more pronounced 2 to 6 mm away from the inoculation point, where no infection was yet established, and suggests that the clones differ in the rate of chitinase-related signal perception or transduction. At 14 days after inoculation, these transcript levels were higher in clone 409 than in clone 589, suggesting that the massive upregulation of class II and IV chitinases after the establishment of infection comes too late to reduce or prevent pathogen colonization.

The first crystal structures of a family 19 class IV chitinase: the enzyme from Norway spruce

“…In Picea abies (Norway spruce), for example, class I, II and IV chitinases are all secreted in response to the plant pathogen Heterobasidion annosum (the causative agent of root and butt rot, the most devastating disease of conifer trees in boreal forests (Hietala et al 2004)), yet how insertions/deletions in the sequences/structures were related to particular biochemical or biological properties remained unknown. Given that coniferous species have such a wide range of commercial uses e.g.…”

Diverse chitinases are invoked during the activity-dormancy transition in spruce

“…In contrast, it is less clear what functional role the putatively non-chitinolytic Pg_GQ03206_D15.1 plays in defense. Wiweger et al (2003) and Hietala et al (2004) provided evidence that class IV chitinases are involved in developmental events such as programmed cell death and suggested that class IV chitinases with enzymatic activity that are localized to the apoplastic space may also be involved in signalling through generation of N-acetylglucosamine and/or oligonucleotides that in turn trigger changes in gene expression. If this is the case, it is conceivable that the dormancyassociated class IV chitinases identified in this study could be involved in mediating developmental events associated with the activity-dormancy transition.…”

“…Pathogen-responsive chitinases often belong to classes I and IV (e.g., SelaBuurlage et al 1993;Davis et al 2002;Passarinho and de Vries 2002;Hietala et al 2004;Islam et al 2010;Kolosova et al 2014) and generally exhibit diagnostic active site residues (Holm and Sander 1994;Hart et al 1995), CBDs (Iseli et al 1993), and a signal peptide targeting the proteins to the secretory pathway (Nielsen et al 1997).…”

“…Chitinases from many species are strongly induced in plants challenged with fungal or bacterial pathogens (e.g., Lawton et al 1992;Collinge et al 1993;Sela-Buurlage et al 1993;Melchers et al 1994;Mason and Davis 1997;Wu et al 1997;Salzer et al 1997;Büchter et al 1997;Hong et al 2000;Hietala et al 2004). Several chitinases are classified as pathogenesis-related (PR) proteins, making up the PR-3, PR-4, PR-8, and PR-11 groups of these defense-associated proteins (van Loon et al 2006).…”

Plant Antiherbivore Defense in Diverse Environments

“…There are proteins than act as chemical defenses, such as enzymes that degrade components of herbivores such as glucanases and chitinases [62]. Generally, chemical defenses have multiple strategies overlapping that result in a chemical toxic cocktail that stops or destroys an aggressive or virulent attack.…”