A butterfly egg-killing hypersensitive response in Brassica nigra is controlled by a single locus, PEK, containing a cluster of TIR-NBS-LRR receptor genes

Knowledge of plant recognition of insects is largely limited to a few resistance (R) genes against sap-sucking insects. Hypersensitive response (HR) characterizes monogenic plant traits relying on R genes in several pathosystems. HR-like cell death can be triggered by eggs of cabbage white butterflies (Pieris spp.), pests of cabbage crops (Brassica spp.), reducing egg survival and representing an effective plant resistance trait before feeding damage occurs. Here, we performed genetic mapping of HR-like cell death induced by Pieris brassicae eggs in the black mustard Brassica nigra (B. nigra). We show that HR-like cell death segregates as a Mendelian trait and identified a single dominant locus on chromosome B3, named PEK (Pieris  egg- killing). Eleven genes are located in an approximately 50 kb region, including a cluster of genes encoding intracellular TIR-NBS-LRR (TNL) receptor proteins. The PEK locus is highly polymorphic between the parental accessions of our mapping populations and among B. nigra reference genomes. Our study is the first one to identify a single locus potentially involved in HR-like cell death induced by insect eggs in B. nigra. Further fine-mapping, comparative genomics and validation of the PEK locus will shed light on the role of these TNL receptors in egg-killing HR.

Population divergence in nutrient-temperature interactions in Pieris rapae

The interaction between larval host plant quality and temperature can influence the short-term physiological rates and life-history traits of insect herbivores. These factors can vary locally, resulting in local adaptation in responses to diet and temperature, but the comparison of these interactions between populations is infrequently carried out. In this study, we examine how the macronutrient ratio of an artificial diet determines the larval growth, development, and survival of larval Pieris rapae (Lepidoptera: Pieridae) at different temperatures between two invasive North American populations from different climatic regions. We conducted a fully factorial experiment with three temperature treatments (18°C, 25°C, and 32°C) and three artificial diet treatments varying in terms of the ratio of protein to carbohydrate (low protein, balanced, and high protein). The effects of diet on life-history traits were greater at lower temperatures, but these differed between populations. Larvae from the subtropical population had reduced survival to pupation on the low-protein diet in the cold temperature treatment, whereas larval survival for the temperate population was equally high for all temperature and diet treatments. Overall, both populations performed more poorly (i.e., they showed slower rates of consumption, growth, and development, and had a smaller pupal mass) in the diet with the low protein ratio, but larvae from the temperate population were less sensitive to diet ratio changes at all temperatures. Our results confirm that the physiological and life-history consequences of imbalanced nutrition for insect herbivores may depend on developmental temperatures, and that different geographic populations of P. rapae within North America vary in their sensitivity to nutritional balance and temperature.