## 3 Discussion
### Facing Host Defenses  
Plant-parasitic nematodes produce a range of antioxidant proteins to evade plant defense responses during infection [7; 51]. We found only one catalase gene (_Mg705_) highly expressed in J2s and until 8 dpi in resistant rice compared to susceptible plants where expression ceases after 2 or 4 dpi. The _M. incognita_ homolog of the catalase gene (_Minc10184-Minc3s00005g00340_) was also up-regulated during the resistance response of _Mi_-expressing tomato [17]. It is likely that they play a role in detoxification by protecting the nematode cells from oxidative damage by ROS, namely H2O2 that may be produced during root invasion. However, it seems that _M. graminicola_ did not display a stronger detoxification strategy when infecting resistant plants as compared to susceptible plants. In the resistant rice TOG5681-_M. graminicola_ interaction, resistance expresses at several infection stages, reducing J2s penetration, giant cell expansion and further female development, and HR-like cell death was not observed [22]. The level of ROS production in response to nematode attack may be similar in resistant and susceptible rice plants and may not fully explain the resistance of TOG5681. In contrast, [PERSON] et al. [17] highlighted the expression of several RKN genes involved in cytoskeleton and starvation stress-induced apoptosis in addition to detoxifying enzymes in the resistant tomato host. Expression of the _Mi_ resistance gene in tomato induces localized cell death when J2s attempt to establish a feeding site [52] and might therefore kill some larvae inside roots. Here, we did not observe specific changes in expression of cytoskeleton and starvation-related genes in _M. graminicola_ when infecting the resistant rice, which is consistent with an absence of HR-like response. It will be interesting to investigate whether similar expression trends would be conserved in other rice (_O. sativa_) genotypes displaying partial or full _M. graminicola_ resistance recently described [18; 19; 20].  
Transcriptomic analyses showed that rice genes predicted to be involved in defence responses, phenylpropanol and hormone pathways were strongly induced from 2 dpi and later on in TOG5681, in contrast to the susceptible plants where these genes were induced later and less strongly [22]. At 2 dpi, we detected only minor differences in the transcriptomes of nematodes infecting resistant or susceptible rice plants but major changes occurred at 4 dpi (119 DEGs-RvsS) and 8 dpi (299 DEGs-RvsS) indicating an effect of the plant genotype on the nematode gene regulation. In fact, the majority of the DEGs-RvsS activated in the resistant rice were genes already expressed by pre-J2s that lowered or totally ceased their expression in the susceptible rice. These genes were almost all involved in the plant invasion process (cell wall-degrading or -modifying enzymes, neuropeptides), and detoxification or evasion of plant defense responses. Thus, our data suggest that these genes are required at an early RKN stage for infecting the plant, irrespective of their level of resistance to the nematode.  
By taking into account the transcriptomic analysis of pre-J2s, our study also provides with valuable understanding of changes that appear in the nematodes in the very first days after infecting a resistant or susceptible host plant, rather than merely highlighting changes occurring between contrasted host genotypes. For instance, [PERSON] et al. [17] discussed up-regulation of _M. incognita_ genes related to cell-wall degradation and peptidases in the resistant tomato cultivar. In the same way, [PERSON] et al. [50] stated that nematode genes critical for _P. penetrans_ development and encoding collagen proteins were down-regulated during infection of the resistant alfalfa cultivar. However, knowledge of gene expression in the pre-infective stage would be required to verify if the same pattern occurred for _M. incognita_, _P. penetrans_ and _M. graminicola_.