Abstract text: Plants are sessile organisms that have developed strategies to cope with various environmental challenges throughout their life cycle. In most natural accessions of Arabidopsis thaliana, temperature changes have been observed to influence seed traits, such as endosperm proliferation and seed size. However, it remains unclear of how seeds perceive temperature cues and regulate the temperature responses. Brassinosteroids (BRs), a class of plant hormones, are promising candidates in this process since BRs play pivotal roles in seed development and regulate phenotypic plasticity in diverse plant tissues. Therefore, we have selected BR genes as candidates to study seed phenotypic plasticity in response to temperature. Consistently, we have observed attenuation of temperature-induced seed traits in BR mutants, including reduced seed sizes and less endosperm proliferation. Interestingly, a transcriptional analysis using bulk RNA-seq has indicated changes of cell wall properties of seed coats in response to different temperatures, and BRs seem to be involved in this response. We are thus assessing the temperature-induced dynamics of cell wall organization in seeds and hypothesize that the status of the seed coat cell walls contributes to several seed traits. This study improves our understanding of seed developmental plasticity, thereby facilitating crop engineering for diverse environmental conditions.