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Abstract

Root-knot  nematodes  (RKN)  are  obligate  endoparasites  that  maintain  a  biotrophic  relationship with  their  hosts  over  a  period  of  several  weeks.  They  infect  roots  as  microscopic  vermiform second-stage  juveniles  (J2)  and  migrate  between  cells  to  reach  the  plant  vascular  cylinder.  To further develop and molt into a pear-shaped female that will release hundreds of eggs on the root surface,  J2s  need  to  successfully  establish  and  maintain  specialized  feeding  struc tures  called “giant-cells” from which they withdraw water and nutrients. Our project aims to identify RKN genes specifically involved in plant parasitism with an emphasis on genes encoding new secreted effectors.  Using  Illumina  RNA-seq  technologies,  we  compared transcriptomes  of  Meloidogyne incognita  during  its  life  cycle  and  identified  genes  over-expressed  in  early  parasitic  stages  as compared to pre-parasitic juveniles (J2s), eggs, females and males. Once the over-expression of selected genes in parasitic  stages was confirmed by RT-qPCR, in situ  hybridizations were carried out to localize the candidates in the nematode secretion organs. Furthermore, siRNA soaking was used  to  silence  these  genes  and  study  their  role in pathogenicity.  In  parallel,  we  are also comparing the transcriptomes of  M. incognita with those of another RKN species that reproduces by  obligatory parthenogenesis,  M.  enterolobii.  This  nematode  represents  a  new  threat  for  the agriculture worldwide because of its ability to reproduce on the majority of known RKN-resistant plants. This comparison will allow us to identify, not only the common set of effectors, but also those specific to one of the other RKN species and possibly involved in host range differences.