RICE / nematodes Interactions

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)

 

 

 

People:

 

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)
 

Scientific Background:

 

    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 infection.

    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 nematode infection.

    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.

Scientific Objectives:

 

The objectives of this project are as follows:

·       To gain knowledge about the molecular mechanisms of specific root developmental changes induced by nematodes.

·       To identify key genes (nematode and rice) involved in feeding site and gall development in roots.

·       To characterize virulence genes encoded by nematodes and their allelic variation in field populations

·       To develop resistance against nematodes using essential nematode genes and RNAi strategy

Program:

 

Functional analysis of nematode secreted proteins.

               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.

Mobility Planning

 
    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.
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