download report - Istituto Pasteur

P a r t i c i p a n t s :
Giulia De Lorenzo, Daniela Bellincampi, professors;
Simone Ferrari, Benedetta Mattei, researchers;
Manuela Casasoli, Francesca Sicilia, Roberta Galletti,
Vincenzo Lionetti, post-doc fellows; Francesco Spinelli,
Fedra Francocci, Lorenzo Mariotti, Manuel Benedetti,
Daniel Savatin, PhD students; Lucia Tufano, graduate student;
Giovanni Salvi, Daniela Pontiggia, technicians.
Report of activity
Plants are continually exposed to pathogens and, in
most cases, successfully defend themselves. Knowledge
of the mechanisms underlying their defense ability
paves the way to improvement of crop resistance. A
sophisticated surveillance system detecting the presence
of pathogens is interconnected with the plant
defense signalling pathways that lead to the activation
of defense responses. The cell wall plays an instrumental
role in the plant surveillance system by releasing
oligosaccharide fragments (oligolacturonides=OGs)
that trigger the typical responses elicited
by PAMPs (Pathogen Associated Molecular Patterns).
The formation of OGs takes place during the degradation
of homogalacturonan by microbial polygalacturonases
(PGs) and is favoured when PGs interact with
specific plant cell wall proteins (polygalacturonaseinhibiting
proteins or PGIPs). Micromolar concentrations
of OGs activate the expression of defense genes
via a signal transduction pathway that functions independently
of the known pathways involving salicylic
acid (SA), jasmonate (JA), and ethylene (Et). The characterization
of this novel signalling pathway is a key
feature of our project. Specific tasks of the project are
i) the dissection of the OG signalling pathway and ii)
the development of resistant plants.
Dissection of the OG signalling pathway
OGs induce a variety of plant defense responses and
increase resistance to the necrotrophic fungal pathogen
Principal investigator: Felice Cervone
Professor of Plant Biology
Dipartimento di Biologia Vegetale
Tel: (+39) 06 49912517; Fax: (+39) 06 49912446
felice.cervone@uniroma1.it
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Molecular recognition in biomolecules - AREA 4
Plant innate immunity: cell wall-mediated signalling and
recognition in plant defense
Botrytis cinerea independently of JA-, SA-, and ETmediated
signalling. Microarray analysis showed that
about 50% of the genes regulated by OGs, including
genes encoding enzymes involved in secondary metabolism
have a similar change of expression during B.
cinerea infection. In particular, expression of PHY-
TOALEXIN DEFICIENT3 (PAD3) is strongly upregulated
by both OGs and infection independently of
SA, JA, and ET. OG treatments do not enhance resistance
to B. cinerea in the pad3 mutant. Similarly to OGs,
the bacterial flagellin peptide elicitor flg22 enhances
resistance to B. cinerea in a PAD3-dependent manner,
independently of SA, JA, and ET. Moreover a rapid
induction of gene expression by OGs is also independent
of salicylic acid, ethylene, and jasmonate. OGs
elicit a robust extracellular oxidative burst that is generated
by the NADPH oxidase AtrbohD. However, the
burst is not required for the expression of OG-responsive
genes or for OG-induced resistance to B. cinerea,
whereas callose accumulation requires a functional
AtrbohD. OG-induced resistance to B. cinerea is also
unaffected in powdery mildew resistant4, despite the fact
that callose accumulation is almost abolished in this
mutant. These results indicate that the OG-induced
oxidative burst is not required for the activation of
defense responses effective against B. cinerea, leaving
open the question of the role of reactive oxygen
species in elicitor-mediated defense.
Development of resistant plants
PGs, enzymes that hydrolyze the homogalacturonan
of the plant cell wall, are virulence factors of several
phytopathogenic fungi and bacteria. On the other
hand, PGs may activate defense responses by releasing
OGs perceived by the plant cell. Tobacco
(Nicotiana tabacum) and Arabidopsis (Arabidopsis
thaliana) plants expressing a fungal PG (PG plants)
have a reduced content of homogalacturonan, are
more resistant to microbial pathogens and have constitutively
activated defense responses. Interestingly,
either in tobacco PG or wild-type plants treated with