TRANSCRIPTIONAL AND HORMONAL DEFENCE-GROWTH TRADEOFFS DETERMINE PLANT SURVIVAL AND FITNESS UPON SPIDER MITE INFESTATION
Tetranychus urticae is an important pest that causes severe damage on a wide variety of plants and crops, leading to a substantial loss of productivity. Previous research has focused on the study of Arabidopsis short-term response to T. urticae, but a comprehensive evaluation of the interaction through whole plant life cycle has not been previously studied. Here, through a physiological trait, transcriptomic and hormonomic evaluation we uncovered the molecular pathways directing the interaction of T. urticae during the complete plant life cycle. Upon mite infestation, plant suffers a process of adaptation to cope the stress and survive, led by the establishment of defence-growth trade-offs in the plant. Transcriptional and hormonal evaluation reveal how plant defence response upon mite perception determines the later growth responses and plant survival. In addition, a delay in plant development with a negative effect on plant fitness was observed, being fitness negatively affected with seed ageing.  Taken together, our findings uncover the dynamics regulating plant-mite interactions and determining plant survival and reproductive success, providing new potential targets for improving plant response. Additionally, trade-offs suppose a cost on final plant fitness, demonstrating the underlying impact of the mite on the establishment of the offspring. Overall design: Three-week-old Arabidopsis thaliana Col-0 plants were infested with twenty T. urticae female adults per plant. Control plants without mites were carried out in parallel. Each plant was covered by a cylinder that enabled the correct growth and development of the plant while avoiding the mites to escape from infested to control plants. Plant material from control and mite-infested plants was analysed at specific ontological stages of the plant development, coinciding with 30 min, 24 h, 4 d, 7 d, 12 d and 15 d post-mite infestation (dpi).Plant aerial parts were sampled and frozen. Four biological replicates composed by pools of four plants were used for each time point and condition. Frozen material was thoroughly grinded on liquid nitrogen and total RNA was extracted by means of the RNeasy plant mini kit (Qiagen), and a DNase treatment (Qiagen) following manufacturer´s instructions.