My research interests focus on how plants adapt to environmental stress. My lab activities are a blend of basic research and its application to answering modern agricultural needs as well as applied research aimed at increasing agricultural income in arid zones by adding new crops and developing new agro-techniques. For example, one project involved improving the salt resistance and fruit quality of tomatoes and other vegetable crops while another focused on using highly saline water for developing cash-crop halophytes for potential halophyte growers.
My core research revolves around a unique family of enzymes, nitrate reductase (NR), sulfite oxidase (SO), aldehyde oxidase (AO) and xanthine dehydrogenase (XDH), the members of which contain molybdo-pterin co factors (Moco) as their active centers. Via the analysis of impaired Moco mutants, my work showed that the additional Moco sulfuration step is essential for the activation of XDH and AO and provides a potential regulatory point for XDH and AO activities. Furthermore, these enzymes are induced by salinity, drought and ABA (phyto-hormone), yet affect plant ABA and control the plant’s water status and biomass production when exposed to drought and salinity stresses. Interestingly, each activity has distinct reactive oxygen species (ROS) signatures. Recently, I demonstrated that SO can control sulfur dioxide poisoning in plants. The basic research described above can be applied to answering modern agricultural and ecological needs, including, but not limited to, improved disease control in fruits and vegetables by fumigation with more effective doses of sulfur dioxide, killing pathogens without damaging the fruits/vegetables, and detoxifying the air pollutant sulfur dioxide using SO overexpression plants that are able to convert sulfite into harmless sulfate.
|Abstracts of Current Research:
- A role of XDH in senescence and dark-induced metabolites remobilization
: Using modified XDH mutants in Arabidopsis, we demonstrated that senescence and dark-induced senescence in RNAi plants impaired in XDH modified plants were different from that of wild-type plants. The molecular, biochemical and metabolistic properties of these sensitivities, as well as the interaction of nitrogen and sulfur metabolism, are under study.
- Use of highly saline water for developing cash-crop halophytes for potential halophyte growers : The extensive desalination facilities in the Ramat Negev Desert and Dead Sea areas in Israel will generate both fresh water and large quantities of highly saline brine. Halophytes are the only plants capable of tolerating the salts present in such brines (~0.5 M NaCl). Among these plants, Salicornia, Aster tripolium, and Atriplex excel in evapotranspiration of water and vigor under saline irrigation. All three are consumed fresh as gourmet foods in several European countries. However, the supply is limited because these plants are rarely grown as agricultural crops and must be obtained from wild plants growing along the seashore and salt marshes. In view of the demand for Salicornia and other halophytes in European markets and their ability to grow on saline water, these halophytes could become an important source of income for the farmers. We are developing agro-techniques for year-round production of these halophytes ("sea vegetables") as cash crops that can productively utilize the brackish water as well as the highly saline brine available from natural sources in the region, thereby contributing to preservation of the environment. The results obtained so far reveal that local Salicornia ecotypes grown in greenhouses and irrigated with highly saline water produce well-shaped and good-tasting Salicornia during the winter. Exports for 2007 from the deserts of Ramat Hanegev and the Dead-Sea are projected to be around 400 tons, capable of generating an annual income of $ 2,000,000. In light of Salicornia’s prospects, we hope that Aster and Atriplex will exhibit similarly successful results within 3 years. For the future development of Salicornia, we hope to develop a cost effective land-based marine aquaculture facility based on fabricated wetlands in which Salicornia functions both as an environmentally friendly biofilter and a valuable by-product.
- Sulfite/SO2 detoxifying/assimilation mechanisms in plants : The dual function of the class of MoCo oxidative enzymes in plant metabolism was also demonstrated in the smallest known plant molybdo-enzyme. Recently we showed that SO can produce H2O2, while plants can utilize SO in a sulfite oxidative pathway to cope directly with the toxicity of the air-pollutant sulfite/SO2 and probably indirectly with the H2O2 by-product, in both cases to oxidize sulfite to the non-toxic sulfate. The extent of the contribution of MoCo enzymes to ROS is currently one of the main thrusts of my research activity. The gaseous pollutant SO2 reacts readily with water to form sulfite, which impacts deleteriously on animal and plant health. By modulating the level of sulfite oxidase that catalyzes the transformation of sulfites to the nontoxic sulfate, we showed that Arabidopsis and tomato plants can be rendered either resistant or susceptible to SO2/sulfite. In addition, we showed that the transcript of sulfite reductase (SiR), a chloroplast-localized enzyme that reduces sulfites to sulfides, and other sulfite-requiring enzymatic activities, such as mercaptopyruvate sulfurtransferases (MST1 and MST2) and UDP-sulfoquinovose synthase1 (SQD1), were induced, whereas SO was constitutively expressed and was not significantly induced by SO2. The importance of this research is that the processes of sulfite/SO2 assimilation and detoxification play crucial roles in plant productivity, since in areas where air SO2 levels are restricted by legislation, crop plants suffer from sulfur shortages and therefore, require extra sulfate fertilizer for normal development and yield.
- Brychkova, G., Grishkevich., Fluhr, R. and Sagi, M. . An essential role for tomato sulfite oxidase and enzymes of the sulfite network in maintaining leaf sulfite homeostasis Plant Physiol. 161: 148-164 (2013)
- Ventura, Y. and Sagi, M. . Halophyte crop cultivation: the case for Salicornia and Sarcocornia. Environ. Exp. Bot. : (2013)
- Yarmolinsky, D., Brychkova, G., Fluhr, R. and Sagi, M. . Sulfite Reductase Protects Plants against Sulfite Toxicity. Plant Physiol. 161: 725-743 (2013)
- Ventura, Y., Myrzabayeva, M., Alikulov, Z., Cohen, S., Shemer, Z. and Sagi, M. The importance of iron supply during repetitive harvesting of Aster tripolium . Functional Plant Biology : (2013)
- Brychkova, G., Yarmolinsky, D., Fluhr, R. and Sagi, M. . The determination of sulfite levels and its oxidation in plant leaves. Plant Sci. 190: 123-130 (2012)
- Brychkova, G., Yarmolinsky, D. and Sagi, M. . Kinetic Assays for Determining In Vitro APS Reductase Activity in Plants without the Use of Radioactive Substances Plant and Cell Physiology 53: 1648-1658 (2012)
- Brychkova, G., Yarmolinsky, D., Ventura, Y. and Sagi, M. . A Novel In-gel Assay and an Improved Kinetic Assay for Determining In Vitro Sulfite Reductase Activity in Plants. Plant and Cell Physiology 53: 1507-1516. (2012)
- Brychkova, G., Alikulov, Z., Fluhr, R. and Sagi, M.. A critical role for ureides in dark and senescence-induced purine remobilization is unmasked in the Atxdh1 Arabidopsis mutant
The Plant J.
54: 506 (2008)
- Brychkova, G., Xia, Z., Yang, G., Yesbergenova, Z., Zhang, Z., Davydov, O., Fluhr, R. and Sagi, M. . Sulfite Oxidase protects plants against sulfur dioxide toxicity The Plant Journal 50: 696-709 (2007)
- Sagi, M. and Fluhr, R . Production of reactive oxygen species by plant NADPH oxidases. Plant Physiology 141: 336-340 (2006)
- Yesbergenova, Z., Yang, G., Oron, E., Soffer, D., Fluhr , R. & Sagi, M. The plant Mo-hydroxylases aldehyde oxidase and xanthine dehydrogenase have distinct reactive oxygen species signatures and are induced by drought and abscisic acid. Plant J. 42: 862-876 (2005)
- SAGI, M., DAVYDOV, O., ORAZOVA, S., YESBERGENOVA, Z., OPHIR, R., STRATMANN, J.W. & FLUHR, R.
. Plant respiratory burst oxidase homologs impinge on wound responsiveness and development in lycopersicon esculentum. Plant Cell. 16: (3) (2004)
- Sagi, M., Scazzocchio, C. & Fluhr, R. . The absence of molybdenum cofactor sulfuration is the primary cause of the flacca phenotype in tomato plants. Plant J. 31: 305-317. (2002)
- Sagi, M. & Fluhr, R. . Superoxide Production by plant homologues of the gp91phox NADPH oxidase. modulation of activity by calcium and by tobacco mosaic virus infection. Plant Physiol. 126: 1281-1290. (2001)