title: Localization and Transcriptional Responses ofChrysoporthe austroafricanainEucalyptus grandisIdentify Putative Pathogenicity Factors.
abstract: Chrysoporthe austroafricanais a fungal pathogen that causes the development of stem cankers on susceptibleEucalyptus grandistrees. Clones ofE. grandisthat are partially resistant and highly susceptible have been identified based on the extent of lesion formation on the stem upon inoculation withC. austroafricana.These interactions have been used as a model pathosystem to enhance our understanding of interactions between pathogenic fungi and woody hosts, which may be different to herbaceous hosts. In previous research, transcriptomics of host responses in these two clones toC. austroafricanasuggested roles for salicylic acid and gibberellic acid phytohormone signaling in defense. However, it is unclear how the pathogen infiltrates host tissue and which pathogenicity factors facilitate its spread in the two host genotypes. The aim of this study was to investigate these two aspects of theE. grandis-C. austroafricanainteraction and to test the hypothesis that the pathogen possesses mechanisms to modulate the tree phytohormone-mediated defenses. Light microscopy showed that the pathogen occurred in most cell types and structures within infectedE. grandisstem tissue. Notably, the fungus appeared to spread through the stem by penetrating cell wall pits. In order to understand the molecular interaction between these organisms and predict putative pathogenicity mechanisms ofC. austroafricana, fungal gene expression was studiedin vitroandin planta. Fungal genes associated with cell wall degradation, carbohydrate metabolism and phytohormone manipulation were expressedin plantabyC. austroafricana. These genes could be involved in fungal spread by facilitating cell wall pit degradation and manipulating phytohormone mediated defense in each host environment, respectively. Specifically, thein plantaexpression of anent-kaurene oxidaseandsalicylate hydroxylaseinC. austroafricanasuggests putative mechanisms by which the pathogen can modulate the phytohormone-mediated defenses of the host. These mechanisms have been reported in herbaceous plant-pathogen interactions, supporting the notion that these aspects of the interaction are similar in a woody species. This study highlightsent-kaurene oxidaseandsalicylate hydroxylaseas candidates for further functional characterization.
authors.affiliation: Department of Genetics, Forestry and Agricultural Biotechnology Institute, Genomics Research Institute, University of Pretoria Pretoria, South Africa.
authors.forename: Ronishree
authors.initials: R
authors.lastname: Mangwanda
authors.affiliation: Department of Genetics, Forestry and Agricultural Biotechnology Institute, Genomics Research Institute, University of Pretoria Pretoria, South Africa.
authors.forename: Lizahn
authors.initials: L
authors.lastname: Zwart
authors.affiliation: Department of Genetics, Forestry and Agricultural Biotechnology Institute, Genomics Research Institute, University of Pretoria Pretoria, South Africa.
authors.forename: Nicolaas A
authors.initials: NA
authors.lastname: van der Merwe
authors.affiliation: Department of Microbiology and Plant Pathology, Forestry and Agricultural Biotechnology Institute, University of Pretoria Pretoria, South Africa.
authors.forename: Lucy Novungayo
authors.initials: LN
authors.lastname: Moleleki
authors.affiliation: Department of Plant and Soil Sciences, Forestry and Agricultural Biotechnology Institute, Genomics Research Institute, University of Pretoria Pretoria, South Africa.
authors.forename: Dave Kenneth
authors.initials: DK
authors.lastname: Berger
authors.affiliation: Department of Genetics, Forestry and Agricultural Biotechnology Institute, Genomics Research Institute, University of Pretoria Pretoria, South Africa.
authors.forename: Alexander A
authors.initials: AA
authors.lastname: Myburg
authors.affiliation: Department of Genetics, Forestry and Agricultural Biotechnology Institute, Genomics Research Institute, University of Pretoria Pretoria, South Africa.
authors.forename: Sanushka
authors.initials: S
authors.lastname: Naidoo
keywords: cell wall degrading enzymes; dual RNA-sequencing; fungal pathogenicity; hormone signaling