Project description:White root rot disease caused by Rosellinia necatrix is one of the most important pathogens affecting avocado productivity in temperate, tropical and subtropical climates. Control of this disease is complex and nowadays, lies in the use of physical and chemical methods, although none have proven to be fully effective. Detailed understanding of the molecular mechanisms underlying white root rot disease has the potential of aiding future developments in disease resistance and management. In this regard, this study used RNAseq technology to compare the transcriptomic profiles of R. necatrix during infection of susceptible avocado `Dusa´ roots with that obtained from the fungus cultured in rich medium. The transcriptomes from three biological replicates of R. necatrix colonizing avocado roots (RC) and R. necatrix growing on potato dextrose agar media (PDA) were obtained using Illumina sequencing. A total of 12,104 transcripts were obtained, among which 1937 were differentially expressed genes (DEG), 137 exclusively expressed in RC and 160 and PDA. Interestingly genes involved in the production of fungal toxins, detoxification of toxic compounds, hormone biosynthesis, gene silencing and plant cell wall degradation were overexpressed during the infection process. In addition, 23 out of the 137 contigs, only expressed during R. necatrix growth on avocado roots, were predicted as candidate effector proteins (CEP) by the CSIRO tool with a probability above 60%. The PHI (Pathogen Host Interaction) database revealed that 11 R. necatrix CEP were previously annotated as effectors genes proven experimentally via pathogen-host interaction.
Project description:Background: Rosellinia necatrix is the causal agent of avocado white root rot (WRR). Control of this soil-borne disease is difficult and tolerant rootstocks may represent an effective method to lessen its impact. To date, no studies on molecular mechanisms regulating the avocado plant response towards this pathogen have been undertaken. To shed light onto the mechanisms underpinning disease susceptibility and tolerance, molecular analysis of the gene's response of two contrasting-disease-reaction avocado rootstocks was assessed. Results: Gene expression profiles against R. necatrix were assessed in the susceptible 'Dusa' and the tolerant selection BG83 avocado genotypes by micro-array analysis. In 'Dusa', the early response is mainly related to redox processes and cell-wall degradation activities, all becoming more remarkable after disease progression affected photosynthetic capacity; whereas, tolerance to R. necatrix in BG83 relies on the induction of protease inhibitors and their negative regulators, as well as salt and osmotic stress related genes besides oxido-reduction processes. We identified three protease inhibitors, glu protease, trypsin and endopeptidase inhibitors, highly overexpressed in the tolerant genotype, when compared to susceptible 'Dusa', after infection with R. necatrix, reaching fold change values of 44, 34 and 16 respectively. Conclusions: The contrasting results between 'Dusa' and BG83 give new insights into the different mechanisms involved in the avocado tolerance to P. cinnamomi and R. necatrix, which are consistent with their biotrophic and necrotrophic lifestyles, respectively. The differential induction of genes involved in salt and osmotic stress in BG83 could indicate that R. necatrix penetration into the roots is associated with osmotic effects suggesting that BG83's tolerance to R. necatrix is related to the ability to withstand osmotic imbalance. In addition, the high expression of protease inhibitors in tolerant BG83 compared to susceptible 'Dusa' after infection with the pathogen, suggests the important role that these proteins could play in the defence of avocado rootstocks against R. necatrix.