Constitutive BoHAK5 expression and early robust induction of salicylic acid biosynthesis genes as candidates to explain the tolerance of broccoli to limiting potassium

Potassium (K⁺) is vital for optimum plant growth and crop yield, and it is an important component of fertilizers. However, our knowledge of the physiological and molecular response to limiting K⁺ conditions is incomplete. Despite their close phylogenetic relationship, we observed that broccoli is more tolerant to limiting K⁺ conditions than Arabidopsis. For this reason, we performed a detailed physiological and transcriptomic analysis to compare and contrast their response to this abiotic stress. Our results show that the K⁺ content of broccoli roots decreases at a slower rate than Arabidopsis. Both species exhibited characteristic responses observed in other plants, such as those related to oxidative stress, hypoxia and jasmonic and abscisic acid signaling. However, we observed notable differences in their responses, especially in the expression of BoHAK5 and the early and strong induction of isoforms of salicylic acid (SA) biosynthesis genes in broccoli, which was reflected in the increased SA accumulation in broccoli leaves. We also observed alterations in the gene expression patterns of enzymes and in the levels of intermediates involved in the biosynthesis of glucosinolates, which are important molecules contributing to the added nutritional value of broccoli. Lastly, we provide evidence for concomitant alterations in the expression patterns of genes encoding transporters of several other ions, such as Fe²⁺, PO₄³⁻ and NO₃⁻. Our data provide insight into the possible mechanisms of broccoli’s tolerance to limiting K⁺ conditions and identify specific targets for the development of crop plants with reduced fertilization requirements.