Rosellinia necatrix infection induces differential gene expression between tolerant and susceptible avocado rootstocks

Abstract

Rosellinia necatrix is the causal agent of avocado white root rot (WRR). Control of this soil-borne disease is difficult, and the use of tolerant rootstocks may present an effective method to lessen its impact. To date, no studies on the molecular mechanisms regulating the avocado plant response towards this pathogen have been undertaken. To shed light on the mechanisms underpinning disease susceptibility and tolerance, molecular analysis of the gene’s response in two avocado rootstocks with a contrasting disease reaction was assessed. Gene expression profiles against R . necatrix were carried out in the susceptible ‘Dusa’ and the tolerant selection BG83 avocado genotypes by micro-array analysis. In ‘Dusa’, the early response was mainly related to redox processes and cell-wall degradation activities, all becoming enhanced after disease progression affected photosynthetic capacity, whereas tolerance to R . necatrix in BG83 relied on the induction of protease inhibitors and their negative regulators, as well as genes related to tolerance to salt and osmotic stress such as aspartic peptidase domain-containing proteins and gdsl esterase lipase proteins. In addition, three protease inhibitors were identified, glu protease, trypsin and endopeptidase inhibitors, which were highly overexpressed in the tolerant genotype when compared to susceptible ‘Dusa’, after infection with R . necatrix , reaching fold change values of 52, 19 and 38, respectively. The contrasting results between ‘Dusa’ and BG83 provide new insights into the different mechanisms involved in avocado tolerance to Phytophthora 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 may play in the defence of avocado rootstocks against R . necatrix .

Mild water stress-induced priming enhance tolerance to Rosellinia necatrix in susceptible avocado rootstocks

“…The expression of thirteen defense-related genes on roots of ‘Dusa’ avocado rootstock subjected to mild-WS and severe-WS and one week after re-watering, was analysed by performing a real time quantitative qPCR (qRT-PCRs). This selection included induced genes indicated in previous studies with ‘BG83’ (tolerant to R. necatrix ) and ‘Dusa’ (tolerant to P. cinnamomi ) avocado rootstocks after infection with the soilborne pathogens R. necatrix [43] and P. cinnamomi , respectively [19, 48–50]. In addition to their implication in pathogen defense, some of the selected genes are also involved in salt, oxidative, osmotic and water stress responses (Table 2).…”

“…More concretely, the accumulation of SA induces the transcription of non-expressor of pathogenesis related gene 1 (NPR1) that further activates genes encoding pathogenesis-related (PR) proteins [31, 32], shown to play an important role in either biotic [33–37] or abiotic stress [38–42] responses. Particularly, avocado tolerance to P. cinnamomi and R. necatrix has been linked to the induction of PR-genes and protease inhibitors, respectively [19, 43]; both are related with other abiotic stresses such as water stress [44, 45]. Thus, it is possible that exposure to one type of stress (i.e.…”

Transcriptome analysis of the fungal pathogen Rosellinia necatrix during infection of a susceptible avocado rootstock identifies potential mechanisms of pathogenesis

“…Neither chemical nor physical methods have proven to be fully effective to control this disease due to the capacity of the fungus to survive in acidic soils as well as to colonize numerous hosts; in addition, the pathogen is quite resistant to drought [4,7]. Nowadays, the obtainment of tolerant rootstocks appears as the most promising approach to control this disease and efforts are underway to reach this goal [10].…”

Transcriptome analysis of the fungal pathogen Rosellinia necatrix during infection of a susceptible avocado rootstock identifies potential mechanisms of pathogenesis

“…Control of this disease is complex due to the pathogen's features (resistance to drought, survival capacity in acidic soils, colonization of numerous hosts, deep penetration into the soil) and nowadays, lies in the use of physical and chemical methods, although none have proven to be fully effective [4,7]. The utilization of tolerant/resistant rootstocks represent the most promising approach to lessen the impact of this soil-borne pathogen, although to date, no tolerant avocado rootstocks to R. necatrix are commercially available [10].…”