My interest lies in understanding how fungal development and pathogenicity are regulated at the cellular and molecular levels. Current projects are focused on analysis of fungal apoptosis and the role that it plays in disease development.

Our goals are:

• To generate detailed knowledge of fungal apoptotic networks in order to develop novel antifungal compounds that will target the apoptotic machinery
• To determine the role of apoptosis in fungal pathogenicity

Specific topics:

• Genomic and bioinformatics analyses of the plant pathogen Botrytis cinerea to identify proteins of the apoptotic network.
• Elucidating the roles of specific apoptotic proteins using genetic, molecular and biochemical approaches:
• Screens for identification of compounds that target the fungal apoptotic machinery and might be used for development of novel antifungal drugs

Additional projects:

• Genetic analysis of Botrytis-Arabidopsis interaction
• Regulation of spore germination
• A server for identification of fungal proteins. We have developed a database and an automated search program to identify fungal homologs of proteins and domains from other organisms. You are welcome to try it at the following link:

http://fastml.tau.ac.il/HomologySearch/

Our fungi

We are working with two plant pathogenic fungi - the grey mold fungus Botrytis cinerea and the anthracnose fungus Colletotrichum gloeosporioides.

Botrytis cinerea is an economically important, cosmopolitan, plant pathogen capable of infecting over 200 plant species. It has a necrotrophic life style and induces programmed cell death (PCD) in the attacked plants. This ability to induce PCD in plants is essential for successful infection.

We have recently shown that during early infection phase, Botrytis is exposed to massive, plant-triggered apoptotic cell death. An anti-apoptotic machinery, mediated by the anti-apoptotic protein BcBir1, is critical for rescue of fungal cells and hence for establishment of infection (Shlezinger et al., 2011).

Colletotrichum gloeosporioides f. sp. aeschynomene (C.g.a) is a hemibiotrophic, host specific pathogen; it is pathogenic only on the weed Aeschynomene virginica and is used for production of the weed-biocontrol product (mycoherbicide) Collego. C.g.a forms special penetration structures (appressoria) that can punch the plant cuticule and are essential for plant infection. Transgenic strains expressing the human anti-apoptotic Bcl-2 protein are stress tolerant, have extended longevity (Barhoom and Sharon, 2007).

Regulation of asymmetric spore germination by Rac1 (Nesher et al., 2011) . When germinated on plants, conidia of Colletotrichum gloesporioides develop asymmetrically; following first mitotic division, only one of the resulting nuclei continue to develop and only a single germ tube is produced (top). Expression of a dominant active allele (DA) of Rac1 affected morphology and development of the fungus (bottom); when conidia of the DA-CgRac1 germinate on plants, nuclei in both cells continue to divide and two germ tubes are produced. ROS gradient and distribution is impaired in the mutants, but there is no change in protein localization.

Apoptosis as target for novel antifungal drugs

Apoptosis is a universal process occurring in almost all living systems. Due to its major role in development and diseases, apoptosis has long been recognized as potential target for cures and a large number of new therapies in human are based on apoptosis-modifying drugs.
In fungi, apoptosis is involved in adaptation to environmental and biological stresses as well as in reproduction and ageing. Fungal apoptosis also can be induced by certain chemicals. Genome sequencing showed that fungi have orthologs of human apoptotic proteins and although these orthologs are usually structurally different from the mammalian counterparts, in general they retain the basic pro- or anti-apoptotic activity.

Thus, fungal apoptotic machinery represents an attractive target for new fungicides: i) it is conserved among all fungi and therefore represents a general target, ii) it is essential for proper fungal development and therefore interference with apoptosis is expected to disrupt fungal development, iii) it can be induced by chemicals, which can be used for development of new fungicides, iv) the proteins regulating fungal apoptosis are sufficiently distinct from their mammalian or plant counterparts, therefore development of selective drugs should be feasible.

Role of apoptosis in pathogenicity

Recent studies support the possibility that plants might provoke fungal PCD as a mechanism to deter pathogens. To investigate this possibility we are studying the role of putative apoptotic genes in pathogenicity using Botrytis and Arabidopsis mutants. We have been able to show that B. cinerea undergoes massive programmed cell death during early stages of infection, but then fully recovers upon transition to second phase of infection. Further studies using the fungal mutants in combination with mutant lines of Arabidopsis showed that virulence was fully correlated with ability of the fungus to cope with plant-induced PCD (Shlezinger et al., 2011). Our result show that BcBir1 is major regulator of PCD in B. cinerea and that proper regulation of the host-induced PCD is essential for pathogenesis in this class of pathogens. Due to the general role of PCD in fungi and considering the common strategies of host invasion by pathogens, we propose that host-induced fungal PCD might be a general phenomenon including in human pathogens.

Botrytis cinerea can infect a large number of plant species including Arabidopsis thaliana. Defense compounds, including the phytoalexin camalexin in A. thaliana, induce apoptotic cell death in the fungus (indicated by TUNEL assay, green nuclei, bottom images), thereby restricting disease spreading. Transgenic fungal strains that over express the anti-apoptotic gene BcBir1 and are apoptosis-tolerant (right) undergo less apoptotic cell death on infected plants and are hypervirulent.

Tsavkelova E., Oeser E., Oren-Young L., Israeli M., Sasson Y., Tudzynski B., Sharon A. (2011). Identification and functional characterization of a bacteria-like gene cluster for indole-3-acetamide-mediated IAA biosynthesis in plant-associated  Fusarium species. Fung. Genet. Biol . In Press.

Shlezinger N., Doron A., Sharon A. 2011. Apoptosis in the grey mold fungus Botrytis cinerea : Molecular components and role in pathogenicity. Biochem. Soc. Trans . 39: 1493-1498.

Kokkelink L., Minz A., Al-Masri M., Giesbert S., Barakat R., Sharon A., Tudzynski P. (2011). The small GTPase BcCdc42 effects nuclear division, germination and virulence of the grey mould fungus Botrytis cinerea . Fung Genet Biol. 48: 1012-1019.

Amselem, J., C., van Kan J. et al. (2011). Genomic analysis of the necrotrophic fungal pathogens Sclerotinia sclerotiorum and Botrytis cinerea . PLoS Genet. 7 (8): e1002230.

Shlezinger N., Minz A., Gur Y., Hatam I., Dagdas YF, Talbot NJ. Sharon A. (2011). Host-induced apoptotic fungal cell death drives plant tissue invasion by necrotrophic pathogens . PLoS Path. 7 (8): e1002230.

Nesher I., Minz A., Kokkelnik L., Tudzynski P. and Sharon A . (2011). Regulation of pathogenic spore germination by CgRac1 in the fungal plant pathogen Colletotrichum gloeosporioides . Eukar Cell. 10: 1122-1130.

Finkelshtein A., Shlezinger N., Bunis O. and Sharon A. (2011). Botrytis cinerea BcNma is involved in apoptotic cell death but not in stress adaptation. Fung Genet Biol. 48: 621-630.

Sharon A. (2010). Editor of a volume on : “Molecular and Cell Biology Methods for Fungi” in the book series "Methods in Molecular Biology". Humana Press, USA.

Sharon, A., Finkelshtein, A., Shlezinger, N. and Hatam I. (2009). Fungal apoptosis: function, genes and gene function. FEMS Microbiol. Rev . 33: 833-854.

Sharon A. and Finkelshtein A. (2009). Programmed Cell Death in Fungal-Plant Interactions . In: Hloger Deising, ed. The Mycota XXII, Plant Relationships, volume V, 2 nd edition, pp 219-234.

Chagué V., Maor R. and Sharon A. (2009). CgOpt1, an oligopeptide transporter from Colletotrichum gloeosporioides that is involved in responses to auxin and in pathogenicity. BMC Microbiology. BMC Microbiology 9: 173.

Barhoom, S., Kupiec, M., Xu J-R. and Sharon, A. (2008). Functional characterization of cgCTR2, a vacuole copper transporter that is necessary for germination and pathogenicity in Colletotrichum gloeosporioides. Eukar. Cell 7: 1098-1108.

Nesher I., Barhoom S., and Sharon A. (2008). c ell cycle and cell death are not necessary for plant infection in the fungal plant pathogen Colletotrichum gloeosporioides. BMC Biology 6: 9.

Wang A., Lane S., Tian Z., Sharon A., Hazan I. and Liu H. (2007). Temporal and spatial control of HGC1 expression results in Hgc1 localization to the apical cell of hyphae in Candida albicans. Eukar. Cell 6: 253-261.

Barhoom S. and Sharon A. (2007) Bcl-2 proteins link programmed cell death with growth and morphogenetic adaptations in the fungal plant pathogen Colletotrichum gloeosporioides . Fung. Genet. Biol. 44: 32-43.

Xu J-R., Peng YL., Dickman MB., and Sharon A. (2006) The dawn of fungal pathogen genomics.
Annu. Rev. Phytopathol . 44: 337-366.

Chagué V., Levanoni-Visel D., Siewers V., Schulze Gronover C., Tudzynski P., Tudzynski B. and Sharon A. (2006) Ethylene Sensing and gene activation in Botrytis cinerea : a missing link in ethylene regulation of fungus-plant interactions? Mol. Plant-Microbe Interact . 19: 33–42.

Sharon A., Barakat R., Tudzynski P. and Elad Y. (2004). Phytohormones in Botrytis -plant interactions. In: Y. Elad, B. Williamson, P. Tudzynski and N. Delen eds. Botrytis spp.: A comprehensive treatise. Kluwer Academic Publisher. Pages 163-180.

Maor R., Haskin, S., Kedmi-Levi H. and Sharon A. (2004). Biosynthesis, regulation and in planta auxin production by Colletotrichum gloeosporioides f. sp. aeschynomene . Appl. Environ. Microbiol . 69: 1695-1701.

Barhoom S. and Sharon A. (2004). cAMP regulation of pathogenic and saprophytic fungal spore germination. Fun. Genet. Biol . 41: 317-326.

Maor R., Kosman E., Golobinsky R., Goodwin P. and Sharon A. (2003). PF-IND: probability algorithm and software for separation between fungal and plant sequences. Curr. Genet . 43: 269-302.

Oren L., Ezrati S., Liberman Z., Cohen D. and Sharon A. (2003). Early events in the Fusarium verticillioides -maize interaction characterized by using a green fluorescent protein-expressing transgenic isolate. App. Evir. Microbiol . 69: 1695-1701.

Horowitz S., Freeman, S. and Sharon A. (2002). Use of GFP-Transgenic Strains to study pathogenic and non-pathogenic development in Colletotrichum acutatum. Phytopathology 92: 743-749.

Chagué V., Elad Y., Barakat R., Tudzynski P. and Sharon A. (2002). Ethylene biosynthesis in Botrytis cinerea. FEMS Microbiol . Ecol . 40: 143-149.

Tudzynski B. and Sharon A. (2001). Biosynthesis, biological role and application of fungal phytohormones. In: H.D. Osiewacz ed. The Mycota, Industrial applications, Vol. X, pp 183-211. Springer-Verlag, Berlin.

Freeman S., Horowitz S. and Sharon A. (2001). Pathogenic and nonpathogenic lifestyles in Colletotrichum acutatum from strawberry and other plants. Phytopathology 91: 986-992.

Ermolieva S., Sharon A., Hadar R., Ma H. and Horwitz B.A. (1999). A MAP kinase of the corn leaf pathogen Cochliobolus heterostrophus is involved in conidiation, appressorium formation and pathogenicity: diverse roles for MAPK homologs in foliar pathogens. Proc. Natl. Acd. Sci. USA. 96: 13542-13547.

Robinson M., and Sharon A. (1999). Transformation of the bioherbicide Colletotrichum gloeosporioides f. sp. aeschynomene by electroporation of germinated conidia. Curr. Genet. 36: 98-104.

Horwitz B.A., Sharon A., Lu S., Yoder O.C. and Turgeon B.G. (1999). A G protein a subunit gene is involved in appressorium formation and mating of Cochliobolus heterostrophus . Fung. Genet. Biol . 26: 19-32.

Robinson M., Riov J. and Sharon A. (1998). Indole-3-acetic acid biosynthesis in Colletotrichum gloeosporioides f. sp. aeschynomene . App. Environ. Microbiol. 64: 5030-5032.

Maor R., Puyesky M., Horwitz B.A. and Sharon A. (1998). Use of the green fluorescent protein (GFP) for studying development and fungal-plant interaction in Cochliobolus heterostrophus. Mycol. Res. 102: 491-496.