Contrasting defence mechanisms against spider mite infestation in Cyanogenic and Non-Cyanogenic legumes

Understanding the complex interactions between plants and herbivores is essential for improving crop resistance. To deep into the role of cyanogenesis in plant defence, we investigated the response of the cyanogenic Phaseolus lunatus (lima bean) and the non-cyanogenic Phaseolus vulgaris (common bean) to Tetranychus urticae infestation. Despite spider mite infesting both legumes, severity of leaf damage was reduced in lima bean. Comparative transcriptome analysis revealed that both species exhibited substantial metabolic and transcriptional changes upon infestation, yet the response in P. lunatus was significantly more pronounced. Specific differences in amino acid homeostasis and in the expression of key genes of the cyanogenic pathway were observed in P. lunatus. Moreover, the mandelonitrile lyase gene (PlMNL1) was upregulated following T. urticae feeding concomitantly to an enzyme activity increase. Lima bean plants also displayed an induction of β-cyanoalanine synthase (PlCYSC1), a key enzyme for cyanide detoxification, suggesting an internal regulatory mechanism to manage the toxicity of their defence responses. These findings contribute to have a major comprehension of the plant-insect interactions and underscore the potential role of cyanogenesis in the elaboration of unique specific defensive responses, even within the same genus, which may reflect distinctive evolutionary adaptations or varying metabolic capabilities between species. To understand the genetic regulation of the differential responses between P. vulgaris and P. lunatus to mite infestation, RNA sequencing (RNA-seq) was performed on leaves from both species 24 hours post T. urticae infestation.