ABC1K2 is involved in stress response and secondary metabolism during seed development in Arabidopsis thaliana

ABC1K2 links stress response and seed development. The Activity of BC1 complex Kinases (ABC1K) family comprises atypical protein kinases with a conserved ABC1 domain and widespread distribution across life domains. In plants, ABC1Ks are predominantly localised in chloroplasts and mitochondria and have been implicated in energy metabolism, abiotic stress response, and developmental processes. Despite growing evidence of their biochemical activity, the functions of many ABC1Ks remain unclear. This study focuses on Arabidopsis thaliana ABC1K2, a plastidial clade member. ABC1K2 is principally localised in seeds; although it shows low expression in vegetative tissues, its transcription is induced by abscisic acid and stress. Functional analysis of abc1k2 mutants and overexpression lines reveals no major effects on plant development or fertility; however, mutant seeds exhibit increased size, mass, and altered pigmentation, along with reduced ABA levels and modified glucosinolate profiles. Transcriptomic data suggest that ABC1K2 integrates developmental signals with stress responses and secondary metabolism, particularly during seed development and germination. This work highlights a novel role for ABC1K2 in linking hormonal regulation and secondary metabolite biosynthesis, offering new insight into the functional diversification of the ABC1K protein family in plants.