Unravelling the secrets of non-host resistance in plant-insect interactions.

Despite the existence of over half million species of plant-eating insects, our planet remains predominantly green. In fact, susceptibility to herbivory is the exception, as plants are resistant to most insect species. This phenomenon is known as nonhost resistance (NHR), where every individual of a plant species is resistant to all variants of a pest or pathogen. While NHR represents the most common and durable outcome of the plant immune system, several aspects of this type of plant defence remains elusive, particularly in plant-insect interactions. In this review, we clarify the concepts of NHR in plant-insect interaction. We emphasize that NHR is a phenomenon arising as a consequence of effective plant defences providing invulnerability to most insect herbivores. This underscores that NHR is one of the main ecological features delimiting the range of plant-insect interactions on Earth. We further highlight the traits and molecular components of the plant immune system known to participate in NHR against insects. Finally, we discuss how NHR can be leveraged as a tool to develop pest resilient crops. Given the significant threat insects pose to global food security, research in plant NHR represents a crucial focal point with immense potential for ensuring food security worldwide.