Iron-induced Transcriptional and Microbiome Changes in Host Roots Associated with Drought Tolerance in Sorghum

Iron (Fe) metabolism is linked to drought tolerance, and to microbial community composition, by unknown mechanisms. In this growth incubator study, exogenous Fe caused a significant recovery from growth retardation in sorghum exposed to drought, including improved photosynthetic attributes. The elevation of Fe in roots of Fe-treated plants was correlated with increased SbFER1 ( Ferritin 1 ) expression, elevated siderophore levels, and decreased H ₂ O ₂ , suggesting that ferritin minimizes oxidative stress under drought. RNA-sequencing analysis in roots demonstrated the Fe-associated induction of genes associated with auxin transport, plus increased indole-3-acetic acid and abscisic acid. Amplicon sequencing indicated alterations of both bacterial and fungal communities in roots by both drought and added Fe. Among fungi, drought reduced Curvularia and Pseudallescheria regardless of Fe levels, while Taralomyces increased with drought but declined when Fe was augmented during drought. Trichoderma levels remained similar under control and drought conditions but dramatically decreased with elevated Fe. In 16S analysis, drought caused a massive increase in Trinickia , which is further amplified by Fe treatment, while the significant increase in Burkholderia by drought was minimized by Fe treatment. The substantial decrease in Herbaspirillum with drought stress was not reversed by Fe supplementation. The abundance of Streptomyces , a known modulator of plant drought tolerance, did not change dramatically with water stress, but split-root assays suggested that elevated Fe is required for Streptomyces to assist sorghum in recovery from drought. These findings indicate that Fe-mediated drought tolerance in sorghum is linked to ferritin-driven redox regulation and shifts in fungal and bacterial communities.