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A Class IV Chitinase Is Up-Regulated by Fungal Infection and Abiotic Stresses and Associated with Slow-Canker-Growth Resistance to Cronartium ribicola in Western White Pine (Pinus monticola)

In the present study, in a candidate gene approach, a class IV chitinase gene (PmCh4A) of pathogenesis-related family three was cloned and characterized in western white pine (Pinus monticola). PmCh4A chitinase expression in the different organs of healthy seedlings was below levels detectable by western immunoblot analysis using an antibody raised against PmCh4A protein. However, a 27-kDa isozyme of PmCh4A accu mulated in both susceptible and slow-canker-growth (SCG) resistant seedlings after infection by Cronartium ribicola. As with fungal infection, the application of a signal chemical (methyl jasmonate) and a protein phosphatase 1 and 2A inhibitor (okadaic acid) increased the PmCh4A protein accumulation. Furthermore, another 26-kDa isozyme was expressed specifically in SCG resistant seedlings, providing a potential tool for marker-assisted selection in forest breeding. Wounding treatment also induced expression of the protein. These data suggest that the class IV chitinase PmCh4A is involved in the defense response of western white pine to infection and abiotic stresses.