AUTHOR=Naidoo Ronishree , Ferreira Linda , Berger Dave K., Myburg Alexander A., Naidoo Sanushka 

TITLE=The identification and differential expression of Eucalyptus grandis pathogenesis-related genes in response to salicylic acid and methyl jasmonate

JOURNAL=Frontiers in Plant Science

VOLUME=4

YEAR=2013

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2013.00043

DOI=10.3389/fpls.2013.00043

ISSN=1664-462X

ABSTRACT=<p>Two important role players in plant defence response are the phytohormones salicylic acid (SA) and jasmonic acid (JA); both of which have been well described in model species such as <italic>Arabidopsis thaliana</italic>. Several pathogenesis related (PR) genes have previously been used as indicators of the onset of SA and JA signaling in <italic>Arabidopsis</italic>. This information is lacking in tree genera such as <italic>Eucalyptus</italic>. The aim of this study was to characterize the transcriptional response of PR genes (<italic>EgrPR2</italic>, <italic>EgrPR3</italic>, <italic>EgrPR4</italic>, <italic>EgrPR5</italic>, <italic>and EgrLOX</italic>) identified in <italic>Eucalyptus grandis</italic> to SA and methyl jasmonate (MeJA) treatment as well as to qualify them as diagnostic for the two signaling pathways. Using the genome sequence of <italic>E. grandis</italic>, we identified candidate <italic>Eucalyptus</italic> orthologs <italic>EgrPR2</italic>, <italic>EgrPR3</italic>, <italic>EgrPR4</italic>, <italic>EgrPR5</italic>, <italic>and EgrLOX</italic> based on a co-phylogenetic approach. The expression of these genes was investigated after various doses of SA and MeJA (a derivative of JA) treatment as well as at various time points. The transcript levels of <italic>EgrPR2</italic> were decreased in response to high concentrations of MeJA whereas the expression of <italic>EgrPR3</italic> and <italic>EgrLOX</italic> declined as the concentrations of SA treatment increased, suggesting an antagonistic relationship between SA and MeJA. Our results support <italic>EgrPR2</italic> as potentially diagnostic for SA and <italic>EgrPR3</italic>, <italic>EgrPR4</italic>, <italic>and EgrLOX</italic> as indicators of MeJA signaling. To further validate the diagnostic potential of the PR genes we challenged <italic>E. grandis</italic> clones with the fungal necrotrophic pathogen <italic>Chrysoporthe austroafricana</italic>. The tolerant clone showed high induction of <italic>EgrPR2</italic> and decreased transcript abundance of <italic>EgrPR4</italic>. Pre-treatment of the susceptible genotype with 5 mM SA resulted in lesion lengths comparable to the tolerant genotype after artificial inoculation with <italic>C. austroafricana.</italic> Thus expression profiling of <italic>EgrPR2</italic> and <italic>EgrPR4</italic> genes could serve as a useful diagnostic approach to determine which of the two signaling pathways are activated against various pathogens in <italic>Eucalyptus</italic>.</p>