Browsing by Subject "salicylic acid"

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  • Tran, Cuong (Helsingin yliopisto, 2018)
    Salicylic acid (SA) is a well-known phytohormone involved in pathogen defense, development and controlling the cellular redox balance. In response to stresses, Arabidopsis thaliana synthesizes SA in the chloroplasts mainly via the isochorismate (IC) pathway: IC synthase (ICS) uses chorismate to produce IC, which is in turn converted to SA. ICS1 is the rate limiting enzyme in SA biosynthesis. The ICS1 protein localizes in the chloroplasts and contains a chloroplast transit peptide sequence, which is the first 45 amino acids in the N-terminus. Under different light conditions, plants employ different stress defense strategies. In a previous study, wild type (WT) Arabidopsis thaliana ecotype Columbia-0 grown under different light conditions [short day (SD; 8h light/16h dark), long day (LD; 16h light/8h dark) and 12h light/12h dark] was exposed to ozone for 1 hour (350 ppb). In a phosphoproteomic approach to study signaling mechanisms, ICS1 has been found as an in vivo phosphoprotein in ozone-treated plants grown under SD condition by mass spectrometry (MS). To analyze the phosphorylation of ICS1 in vitro, WT and phospho-negative ICS1 proteins were produced recombinantly as GST-fusion proteins in E. coli and used as the substrates for targeted kinase assays. Phospho-negative ICS1 protein was generated by mutating the phospho-sites to alanines by site-directed mutagenesis. ICS1 could be phosphorylated either in the cytosol or in the chloroplasts. Therefore, different cytosolic kinases, which are involved in various stress signaling events, and a chloroplast protein kinase that functions as a dominant regulator of chloroplast processes, were selected as the kinases to be tested. In this study, GST-ICS1 could be successfully phosphorylated in vitro. To a similar extent, GST-phospho-negative ICS1 was phosphorylated, indicating that ICS1 was phosphorylated in vitro at sites that were different from the ones found by MS from plant material. In order to study the identified phospho-sites in vivo, transgenic Arabidopsis carrying WT, phospho-positive, and phospho-negative ICS1 proteins were generated. Transgenic plants were confirmed by genotyping. Western blotting was carried out to evaluate ECFP-WT ICS1 protein expression. However, none of the transgenic plants could be confirmed to carry ECFP-WT ICS1. Additionally, an antibody against AtICS1 produced by the company Agrisera was tested for its specificity against the endogenous ICS1 protein. While the antibody could detect recombinant GST-ICS1 protein, ICS1 could not be detected from a total protein extract.
  • Vuorinen, Katariina; Zamora, Olena; Vaahtera, Lauri; Overmyer, Kirk; Brosché, Mikael (2021)
    Plants require interaction between signaling pathways to differentiate and integrate stress responses and deploy appropriate defenses. The hormones ethylene, salicylic acid (SA), and jasmonic acid (JA) are important regulators of plant defenses. Numerous interactions between these signaling pathways are the cornerstone of robust plant immunity. Additionally, during the early response to pathogens, reactive oxygen species (ROS) act as signaling molecules. Here, we examined the extent of signal interaction in the early stages of Botrytis cinerea infection. To enable a comparison between B. cinerea infection with ROS signaling, we subjected plants to ozone treatment, which stimulates an apoplastic ROS burst. We used a collection of single, double, and triple signaling mutants defective in hormone signaling and biosynthesis and subjected them to B. cinerea infection and ozone treatment at different timepoints. We examined lesion size, cell death, and gene expression (both quantitatively and spatially). The two treatments shared many similarities, especially in JA-insensitive mutants, which were sensitive to both treatments. Unexpectedly, a B. cinerea- susceptible JA-insensitive mutant (coil), became tolerant when both SA biosynthesis and signaling was impaired (coil npr1 sid2), demonstrating that JA responses may be under the control of SA. Extensive marker gene analysis indicated JA as the main regulator of both B. cinerea and ozone defenses. In addition, we identified the transcription factor SRI_ as a crucial regulator of PLANT DEFENSIN expression and cell-death regulation, which contributes to resistance to B. cinerea. Overall, our work further defines the context of ROS in plant defense signaling.
  • Mariotti, Lorenzo; Huarancca Reyes, Thais; Ramos-Diaz, Jose Martin; Jouppila, Kirsi; Guglielminetti, Lorenzo (2021)
    Increased ultraviolet-B (UV-B) due to global change can affect plant development and metabolism. Quinoa tolerates extreme conditions including high UV levels. However, the physiological mechanisms behind its abiotic stress tolerance are unclear, especially those related to UV-B. We previously demonstrated that 9.12 kJ m−2 d−1 may induce UV-B-specific signaling while 18.24 kJ m−2 d−1 promotes a UV-B-independent response. Here, we explored the effects of these UV-B doses on hormonal regulation linked to plant morphology and defense among diverse varieties. Changes in fluorescence parameters of photosystem II, flavonoids and hormones (indoleacetic acid (IAA), jasmonic acid (JA), abscisic acid (ABA) and salicylic acid (SA)) were surveyed under controlled conditions. Here, we showed that the sensitivity to short acute UV-B doses in varieties from different habitats is influenced by their parental lines and breeding time. UV-B sensitivity does not necessarily correlate with quinoa’s geographical distribution. The role of flavonoids in the UV-B response seems to be different depending on varieties. Moreover, we found that the extent of changes in JA and SA correlate with UV-B tolerance, while the increase of ABA was mainly related to UV-B stress.