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Physiological and molecular responses of 'Dusa' avocado rootstock to water stress: insights for drought tolerance

ABSTRACT: The aim of this study was to evaluate the physiological response and the expression analysis of `Dusa´ avocado rootstocks subjected to two different levels of water stress, and their subsequent recovery. At the beginning of the experiment, avocado plants were divided in Control plants (watered to field capacity (Fc) throughout the experiment) and stressed plants that were subjected to controlled substrate drying-up until they reached 50% of Fc (mild-WS) and 25% of Fc (severe-WS), respectively. Afterwards, plants were fully irrigated to assess drought recovery response. A set of physiological measurement were taken at leaf and whole-plant levels to assess avocado response to each level of water stress and rewatering. Root samples were collected in mild-WS and severe-WS and gene expression analysis was carried out using a targeted cDNA avocado stress microarray containing transcripts from de novo sequencing of 'Dusa' in response to biotic and abiotic stress. Avocado gene expression profiles under different levels of water stress are discussed in order to shed light on the molecular mechanisms associated with water deprivation in Dusa avocado rootstocks.

ORGANISM(S): Persea americana

PROVIDER: GSE151051 | GEO | 2021/11/03

REPOSITORIES: GEO

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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.

Project description:Transcriptional variation, also called expression level polymorphism (ELP), contributes to intra-specific phenotypic variation in many organisms. Differentially expressed transcripts are typically enriched for stress-related genes, suggesting that differences in response to the environment are a particularly common point of divergence among gentoypes. Analysis of ELPs also has been suggested as a way to assess unintended consequences of transgene introduction; however, it is important that interpretation of transcriptional changes be performed within the context of potential fitness effects. In these studies we sought to examine differential gene expression in response to salinity for two widely used Arabidopsis thaliana ecotypes, Wassilewskija (Ws) and Columbia (Col), and a single gene mutation (glabrous, gl1-1) in the Col background (Col(gl)), in relation to genetic, phenotypic, and fitness differences. Growth analyses were performed with seedlings germinated on culture media and growth chamber-grown plants carried through the full life cycle. Transcriptome analyses were performed with salt treated and control growth-chamber grown plants six days post initiation of salt stress. Ws plants had the least salt injury and highest dry matter accumulation and seed production in salt stressed conditions. ELPs among genoytypes and in response to 100 mM NaCl were enriched for genes associated with response to stress, including stress-associated transcription factors, heat shock and redox metabolism genes, and R genes. Application of salt resulted in many more transcripts up- or down-regulated in Col and Ws than in Col(gl). Many of the transcripts influenced by salt in Col were already altered in gl1-1 plants in the absence of salt, although Col(gl) plants did not show any detectable signs of stress, or effects on fecundity in the absence of salt treatment. The majority of salt-induced transcriptional changes that occurred in Ws also occurred in Col, suggesting common salt stress responses in these two ecotypes. Many more genes were affected by salt in Col than Ws, however, possibly reflecting the greater salt injury observed for Col. There was minimal overlap between the transcripts that differed for Ws and Col prior to salt treatment and those that were subsequently affected by salt stress. Thus, many genes conferring comparative salt stress tolerance in Ws likely differ from those whose expression levels are modified in response to salt stress. These studies demonstrate transcriptional variation among Arabidopsis genotypes in response to salt stress. Greater transcriptome differences did not necessarily correspond with greater genetic difference or phenotypic differences in morphology, fecundity, and resistance to salt stress. These results suggest that depending on circumstance, transcriptional changes can reflect response to injury, facilitate adaptive expression of fitness-associated traits, or allow for phenotypic buffering to minimize the impact of genetic changes.

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Physiological and molecular responses of 'Dusa' avocado rootstock to water stress: insights for drought tolerance

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