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. Aiming to expand 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 (spider mite) infestation. Despite mite infesting both legumes, leaf damage infringed by this feeder was reduced in lima bean. Comparative transcriptome analyses revealed that both species exhibited substantial metabolic and transcriptional changes upon infestation, although alterations in P. lunatus were significantly more pronounced. Specific differences in amino acid homeostasis and key genes associated with the cyanogenic pathway were observed in these species, as well as the upregulation of the mandelonitrile lyase gene (PlMNL1) following T. urticae feeding. Concomitantly, the PIMNL1 activity increased. 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 our understanding of the legume-herbivore interactions and underscore the potential role of cyanogenesis in the elaboration of specific defensive responses, even within the same genus, which may reflect distinctive evolutionary adaptations or varying metabolic capabilities between species.