Abstract
BackgroundPhlomis plants are a source of biological active substances with potential applications in the control of phytopathogens. Phlomis purpurea (Lamiaceae) is autochthonous of southern Iberian Peninsula and Morocco and was found to be resistant to Phytophthora cinnamomi. Phlomis purpurea has revealed antagonistic effect in the rhizosphere of Quercus suber and Q. ilex against P. cinnamomi. Phlomis purpurea roots produce bioactive compounds exhibiting antitumor and anti-Phytophthora activities with potential to protect susceptible plants. Although these important capacities of P. purpurea have been demonstrated, there is no transcriptomic or genomic information available in public databases that could bring insights on the genes underlying this anti-oomycete activity.ResultsUsing Illumina technology we obtained a de novo assembly of P. purpurea transcriptome and differential transcript abundance to identify putative defence related genes in challenged versus non-challenged plants. A total of 1,272,600,000 reads from 18 cDNA libraries were merged and assembled into 215,739 transcript contigs. BLASTX alignment to Nr NCBI database identified 124,386 unique annotated transcripts (57.7%) with significant hits. Functional annotation identified 83,550 out of 124,386 unique transcripts, which were mapped to 141 pathways.39% of unigenes were assigned GO terms. Their functions cover biological processes, cellular component and molecular functions. Genes associated with response to stimuli, cellular and primary metabolic processes, catalytic and transporter functions were among those identified.Differential transcript abundance analysis using DESeq revealed significant differences among libraries depending on post-challenge times.Comparative cyto-histological studies of P. purpurea roots challenged with P. cinnamomi zoospores and controls revealed specific morphological features (exodermal strips and epi-cuticular layer), that may provide a constitutive efficient barrier against pathogen penetration. Genes involved in cutin biosynthesis and in exodermal Casparian strips formation were up-regulated.ConclusionsThe de novo assembly of transcriptome using short reads for a non-model plant, P. purpurea, revealed many unique transcripts useful for further gene expression, biological function, genomics and functional genomics studies.The data presented suggest a combination of a constitutive resistance and an increased transcriptional response from P. purpurea when challenged with the pathogen. This knowledge opens new perspectives for the understanding of defence responses underlying pathogenic oomycete/plant interaction upon challenge with P. cinnamomi.
Highlights
Phlomis plants are a source of biological active substances with potential applications in the control of phytopathogens
A significant reduction of the root rot disease symptoms in Q. suber has been observed when P. purpurea is growing in the tree surroundings which accounts for the importance of the triangular interactions between Phlomis purpurea, Phytophthora cinnamomi and Q. suber/Q. ilex previously reported by Neves et al [5] and Neves [6]
Statistical analysis of measurements taken on 50 samples showed no significant differences (P = 0.095) in the thickness of the radial walls of the exodermis and a significant (P < 0.0001) increase in the thickness of the external tangential root cells walls of plants challenged with Phytophthora cinnamomi (Fig. 1e and f )
Summary
Phlomis plants are a source of biological active substances with potential applications in the control of phytopathogens. Phlomis purpurea roots produce bioactive compounds exhibiting antitumor and anti-Phytophthora activities with potential to protect susceptible plants. These important capacities of P. purpurea have been demonstrated, there is no transcriptomic or genomic information available in public databases that could bring insights on the genes underlying this anti-oomycete activity. Phytophthora cinnamomi is a highly aggressive oomycete that causes root rot disease in thousands of plant species including ornamentals and crop plants as well as fruit and forest trees [2]. This pathogen is the main biotic factor responsible for Quercus suber and Q. ilex subsp. Characterizing changes in gene expression triggered by the pathogen in the resistant P. purpurea plant may contribute to elucidate the mechanisms underlying constitutive defences of P. purpurea against P. cinnamomi infection
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