Gibberellin biosynthesis and DELLA-mediated signalling shape Arabidopsis thaliana responses to the herbivore Tetranychus urticae

Plant defence responses are primarily driven by the ability of plants to perceive stress and activate specific defence strategies that ensure survival, often at the expense of growth and overall fitness. Observed trade-offs between defence and growth suggest that growth-promoting hormones, such as gibberellins (GAs), play a key role in modulating the establishment of appropriate defence responses against biotic stress. In this study, we investigated the role of GAs in the defence response of Arabidopsis thaliana against the two-spotted spider mite ( Tetranychus urticae ) using plants with altered GA levels and modified DELLA protein expression. Under infestation conditions, analyses of plant growth, foliar damage, and spider mite fecundity supported a role for GAs in mediating the trade-off between growth and defence. Specifically, plants with reduced GA content or elevated RGL3 expression exhibited increased resistance to mite attack. Transcriptomic analyses revealed that the reduced damage observed in the ga1 mutant and RGL3 -overexpressing plants was associated with downregulation of genes related to salicylic acid-responsive pathways and upregulation of genes involved in anthocyanin biosynthesis linked to jasmonic acid-mediated responses. These findings underscore the importance of hormonal crosstalk between growth and defence pathways in orchestrating tailored responses to biotic stress, highlighting the pivotal role of GAs in balancing growth and immunity in plants.