Study of nematode virulence effectors and resistance responses in rice -Meloidogyne spp. interactions
(The illustration shows a rice root system after
infection by nematodes, we can observe galls and enlargement of roots that result
of an induced modification of root morphogenesis by nematodes)
Project leaders: Dr. Stephane Bellafiore (IRD), Dr. Ngo Thi Xuyen (HUA)
With: Dr. Diana Fernandez
(IRD), Pr. Do
Nang Vinh (AGI), Pr. Pascal Gantet (UM2/IRD) Dr. Anne-Sophie Petitot (IRD).
PhD Student: Vu Phong Nguyen (Vietnamese Government Scholarship)
Root-knot nematodes (Meloidogyne spp.) are
one of the three most economically damaging genera of plant-parasitic nematodes
on horticultural and field crops. Rice (Oryza sativa) can experience severe
losses from M. graminicola and M. incognita species in Asia and Africa. The toxicity of chemicals used for nematode
control and the low number of available resistance sources urge the need for
alternative and durable control methods.
Meloidogyne spp. are obligate parasites that
settle in roots and complete their life cycle by feeding from root cells. The
nematodes induce the differentiation of root cells into hypertrophied,
multinucleate and metabolically active feeding cells called giant cells. How
these parasites are able to evade host defense responses and establish the
intimate association within the host necessary for feeding and subsequent
reproduction has been a key question over the past 50 years.
It is believed that secretions from the nematode are crucial in invasion and
establishment in the host.
Recently, an exhaustive mass spectrometry analysis of M. incognita secretions
allowed to directly identifying 486 proteins secreted by the nematode.Currently, among the 486 proteins identified by Bellafiore et al.
(2008), a set of 10 proteins were selected based on their enrichment level and
the presence of a signal peptide. Present activities aim at the functional
analysis of the candidate proteins to investigate their role in nematode
In parallel, the identification of plant genes involved
in the response to nematodes remains a major challenge and should greatly
improve our understanding of the metabolic pathways targeted by nematodes to
alter root development and maintain giant cells. Rice (Oryza
sativa) plants are susceptible to Meloidogyne
spp. infection and specific resistances were identified in the African relative
species O. glaberrima. The rice (O. glaberrima) – Meloidogyne spp. interactions thus may serve as a model to understand incompatible
plant- nematode interactions. Current activities involve the genome-wide analysis of rice responses to M. graminicola and M. incognita to identify the metabolic pathways that are altered by
Knowledge about the molecular mechanisms of plant immunity and nematode
pathogenicity will help the incorporation of effective and durable resistance
in rice plants by enhancing the active defence responses or interfering in the
disease processes, opening new avenues for Meloidogyne spp. control
strategies in rice.
objectives of this project are as follows:
gain knowledge about the molecular mechanisms of specific root developmental
changes induced by nematodes.
identify key genes (nematode and rice) involved in feeding site and gall
development in roots.
characterize virulence genes encoded by nematodes and their allelic variation
in field populations
develop resistance against nematodes using essential nematode genes and RNAi
Functional analysis of nematode secreted
Reverse and forward genetic analyses will be conducted
to assess the role of the candidate effector proteins previously identified
during rice-nematode interactions. Assessment of nematode growth and
development on transgenic plants will allow selecting genes involved in
establishing the compatibility with the host plant
Identification of specific plant targets for
nematode virulence proteins.
Pathogen effectors are known to
target root developmental pathways to allow for feeding site differentiation
and successful establishment in the host. Rice mutants impaired in important
developmental pathways will be screened for resistance and phenotypic responses
to Meloidogyne will be assessed at the root level. Rice genes involved
in establishing feeding sites and galls will be further analysed to understand
their function and how they are targeted by the nematode. It will be particularly interesting
to know how the expression of genes involved in normal root morphogenesis could
be modified by nematode effectors to modify root morphogenesis and structure.
Genetic diversity analysis of M. graminicola
field populations in Vietnam
Candidate effectors will be selected for the
analysis of their variability in rice field populations. Insights into allelic
diversity in nematode effector gene loci will reveal mechanisms underlying the
dynamics of adaptation to plant defences in populations of nematodes. This will
help to design conserved siRNA or miRNA to target these genes and to engineer
and test new resistances in planta.
This project will be conducted on both sites:
IRD-Montpellier and LMI/IAG-Hanoi including the contribution of PPRI. A PhD
student from Vietnam will be involved in this project (Mr. Vu Phong Nguyen). With Stephane Bellafiore,they will share his time between France and Vietnam over
4 years in function of the needs of the project development.