Abstract
Selenium (Se) is beneficial for plants and essential for humans, yet it is typically present in the human diet only at trace levels. Agronomic biofortification offers a promising strategy to address this gap. Because Se and sulfur (S) share similar chemical properties and are taken up and assimilated through analogous pathways, sulfur-rich crops are particularly well-suited to Se biofortification. Broccoli, known for its naturally high S content, is therefore a strong candidate for this approach. Techniques such as the pre-application of elements at the seedling stage can modify plant metabolism (priming effect), enhancing their accumulation when the same element is reapplied at the adult stage. This study investigated how seedling priming with Se affects its uptake and assimilation during subsequent foliar biofortification, focusing on the expression of genes involved in the sulfur pathway. A greenhouse experiment was conducted in which broccoli plants were grown to floret production. Three days after the last foliar application, gene expression in the SULTR , APS , and APR families was quantified by RT-PCR, and Se concentration in florets was determined at harvest. Seedling priming was shown to create a more efficient metabolic apparatus, thereby increasing Se uptake by increasing the expression of SULTR1;1 . Following agronomic biofortification, seedling priming led to a significantly greater upregulation of genes involved in Se activation and reduction compared with non-primed plants. This was evidenced by a robust upregulation of APR1 (65-fold) and APS2 (+ 48%), which were directly associated with a marked increase in Se concentration in florets (+ 165%). Our findings suggest that seedling priming establishes a metabolic memory that improves Se assimilation when plants are later biofortified, making it an efficient strategy for agronomic biofortification.