Fluctuation in nitrate availability impacts cytokinin biosynthesis through histone modifications of IPT3 in Arabidopsis roots for growth acclimation

In soil, nitrate availability is variable and often a limiting factor for crop growth. Plants need to acclimate rapidly to fluctuations. The phytohormone cytokinin (CK) plays a pivotal role in nitrate signaling as a secondary growth-regulating signal. However, the mechanisms that regulate CK action in response to fluctuating nitrate levels remain poorly understood. Here, we show that chromatin modification of IPT3, a key gene for cytokinin biosynthesis, is crucial for growth acclimation under fluctuating nitrate environments. The transcriptional regulation of IPT3 drives CK output in response to nitrate availability, thereby controlling the balance of growth between roots and shoots. This rapid and dynamic regulation is mediated by two antagonistic histone H3 modifications: H3K27me3 and H3K4me3. Using mutants impaired in the deposition or removal of these modifications, we identify several chromatin effectors involved and confirm that the chromatin dynamics, influenced by nitrate fluctuation, fine-tune CK biosynthesis. Our findings provide insights into the epigenetic mechanisms regulating CK biosynthesis and open new avenues for enhancing plant acclimation to fluctuating nutritional environments.