Fine-tuning iron acquisition and tolerance: Unraveling the physiological and molecular adaptations of bamboo to iron stress

Iron is essential for plant development, but deviations from optimal levels cause oxidative stress, lower chlorophyll content, and suppress growth. A comprehensive understanding of these mechanisms in bamboo is still lacking. Here, we determined the optimal iron concentration for bamboo growth and assessed the transcriptomic and physiological responses of seedlings at 1, 4, and 8 days after iron stress treatments. Under iron deficiency and toxicity, we identified 7386 and 7848 DEGs, respectively. GO analysis revealed significant enrichment in redox and oxidative stress responses, metal ion transport, and lipid metabolism under both conditions. KEGG analysis indicated that phenylalanine metabolism and flavonoid biosynthesis were associated with ROS, SA- and ABA-mediated pathways. Targeted flavonoid quantification showed that quercetin, kaempferol, and catechin accumulated under iron deficiency and toxicity, whereas homoeriodictyol and naringenin increased only under iron toxicity. Our findings indicate that moso bamboo possesses components associated with both Strategy I and Strategy II iron uptake. Under iron-sufficient conditions, PeNRAMP5 may contribute to basal iron uptake. Under iron deficiency, Strategy I related transporters PeIRT2 and PeNRAMP1 were rapidly induced, followed by the activation of Strategy II related transporters PeYSL15 and PeYSL16, which together participate in iron acquisition and translocation. Yeast one-hybrid and dual-luciferase assays further showed that PePRI1 activates PeIRT2 expression by binding to its promoter. PeIRT2, PeNRAMP1, and PeNRAMP5 restored the growth of the Fe-uptake-defective yeast mutant fet3fet4 , supporting their potential roles in Fe uptake and transport. Moreover, under iron toxicity, most iron uptake-related genes were transcriptionally repressed. The analysis of mineral element contents revealed that varying iron concentrations affect the absorption and transport of other mineral elements in bamboo. This study reveals dynamic physiological, metabolic, transcriptional, and transport strategies underlying bamboo adaptation to iron stress, providing insights for improving nutrient balance and iron tolerance.