Better Late than Never: The Impact of Hatching Time on Heterodera schachtii Parasitism

Plant-parasitic nematodes are a diverse group collectively capable of infecting most major crops. Amongst the most damaging are the cyst nematodes, which can remain dormant in the soil for decades as infection-competent, developmentally arrested, second-stage juveniles in eggs. Hatching is stimulated by a variety of factors. However, the impact of hatching factor responsiveness on nematode morphology, physiology, gene expression, and infection biology has not been explored. We examined the impact of hatching time on the beet cyst nematode, Heterodera schachtii. We found that late hatchers invaded host roots and established feeding sites in greater numbers than early hatchers. We demonstrate variation in baseline parasitism gene expression and in responsiveness of genes to effectostimulins - small, plant-derived molecules which upregulate parasitism genes. Three quarters of effectostimulin-induced transcriptional changes were also modulated, either positively or negatively, by hatching time. While there were no observable morphological differences between early and late hatching nematodes on their day of hatching, the late hatchers displayed signs of faster utilisation of internal energy reserves after 7 days at 4°C, as evidenced by less body area attributed to fat, than early hatchers. Finally, we found no evidence of substantive genetic differences between early and late hatchers - they were representative of a single population, despite the observed differences in infection, gene expression, and physiology. Taken together, non-genetic differences likely drive late hatchers to more rapidly utilise their internal energy reserves, to be differentially responsive to host-derived signals, and to be ultimately more infective than their early hatching counterparts.