Dottoressa di ricerca

ciclo: XXXV

supervisore: Giovanna Serino
co-supervisore: Paola Vittorioso

Titolo della tesi: The effect of sequential abiotic stresses on physiological and molecular defense responses in Arabidopsis thaliana

Plants are constantly exposed to stresses during their lifespan, and they have evolved a sophisticated mechanism to react to multiple stresses known as ‘priming’, this allows a more rapid and robust response to recurring or subsequent stresses. However, while large amounts of work have been put into understanding how plant response to a single type of stress can have long-term consequences on molecular and physiological state and on the subsequent responses to the same stress, considerably less is known on how the priming effect due to one type of stress can help plants cope with a subsequent different type of stress, a situation that can be easily found in natural ecosystems. Among abiotic stresses, drought (D) and high light (HL) contribute significantly to declines in crop productivity, resulting in high economic losses worldwide. Plant responses to D or HL have been already characterized to a detailed degree, but only in experiments in which only one of the two was used as a stress source. Based on this, this work aims at investigating if plant response to one stress can affect its responses to a subsequent stress, by characterizing plant physiological and molecular responses in plants exposed to a short-term stress by HL, followed by a long-term D stress. To study the priming effect, a sequential stress experiment was performed using HL as the first stress and D as the second stress. Gene expression analysis was performed using qPCR to evaluate the transcript level of stress-response genes (RD29A, ABA1, NCED3, AREB1, and DREB2). These genes were chosen because RD29A is a recognized marker gene for the D response, and the others were evaluated since Abscisic Acid (ABA) is recognized as the primary phytohormone in stress responses. Additionally, the two transcription factors, AREB1 (ABA-dependent) and DREB1 (ABA-independent), were examined since the D stress response can cause both ABA-dependent and ABA-independent responses. The results from the gene expression analysis indicates that HL mediates a priming response against D on these genes. Given that HL mediated a priming response on these ABA genes, to gain more insight into 4 ABA involvement in this priming response, the ABA deficient mutant aba1-3 was also used in this study. Altogether, the results suggest that an ABA-dependent and independent response is triggered by this sequential stress exposure and priming is mediated through these two ABA responses. The physiological status of the plants was also monitored by looking at photosynthesis performance, water status, and stomatal conductance. The goal was to determine whether any physiological changes corresponded with gene expression. Photosynthesis performance, water status and stomatal conductance are good indicators to monitor D and HL stress. Photosynthesis performance was evaluated by examining: 1. Fv/Fm ratios using chlorophyll fluorescence imaging 2. Quantum yield of fluorescence using a fluorometer 3. Carbon assimilation using a gas- exchange analyser to calculate the assimilation in real time. The water status was evaluated by using a psychrometer to measure the leaf water potential and stomatal conductance evaluated by using a fluorometer/porometer to measure the rate of CO2 entering and water vapour exiting the stomata. Overall, the result from these physiological measurements suggests that these physiological processes did not experience distinct metabolic changes in response to the stresses and were not taken into consideration for priming. Changes in chromatin structure have been linked to stress memory and priming therefore, this study also explores histone modification, specifically the H3K4me3 mark as a potential stress memory mark that could be activated and play a role in the priming of gene expression. The histone mark was assessed by immunoblotting analysis and the findings suggest that H3K4me3 could be a good candidate as an epigenetic mark in priming and stress memory response, however, further study needs to be performed to assess this mark for its possible function in such response. The overall results in this study provide an initial characterization of how HL can influence the plant response to a subsequent D stress. The findings build on the knowledge of priming in the context of HL and D.

Produzione scientifica

  • 11573/1678806 - 2023 - Highlight Induced Transcriptional Priming against a Subsequent Drought Stress in Arabidopsis thaliana (01a Articolo in rivista)
  • 11573/1685880 - 2021 - From the Outside to the Inside: New Insights on the Main Factors that Guide the Germination Process (01a Articolo in rivista)
  • 11573/1486911 - 2021 - From the outside to the inside: New insights on the main factors that guide seed dormancy and germination (01g Articolo di rassegna (Review))

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