Pathogenesis-related genes and proteins in forest tree species

Trees occupy more than 30% of the land biosphere. They are important from both ecological and environmental standpoints and provide some of the most valuable commodities in the world economy. The perennial nature and size of trees are the critical determinants of their survival in response to biotic and abiotic stresses. The identification of the defense pathways at biochemical and genetic levels in tree pathosystems are beginning to be addressed. The basic physiological and biochemical mechanisms in woody perennials in response to pathogen is homologous to the model annual crop like Arabidopsis, but their secondary metabolic processes and ecological survival strategies are likely to be divergent from their annual counterparts. The limited domestication in tree species makes its molecular mechanisms less comparable to the highly pedigreed crop species. Recent reports have highlighted that the possible difference in genetic programs responding to invasive pathogens between annuals and perennials could be the spatial and temporal pattern of gene regulation. Several reviews on pathogen defense with reference to crop species are available, while similar reports from the tree species are limited to few commercially important species like Populus, Pinus, Picea, Eucalyptus, Castanea, and Pseudotsuga. This paper reviews the present status of pathogenesis-related genes and proteins from tree species with emphasis on the resistant genes and the proteins induced during systemic acquired resistance and highlights the ecological and evolutionary significance of defense-related genes from tree species.