Investigating the mechanism of auxin-mediated fulvic acid-regulated root growth in Oryza sativa through physiological and transcriptomic analyses

Abstract

Background Rice is one of the most important staple dietary constituents worldwide, so improving cultivated rice yields is crucial for global food security. Fulvic acid (FA) is a plant growth promoter and organic fertilizer, and investigating its effects on rice root growth is of great practical significance for improving rice yield and quality. Results This study examined the effects of different FA concentrations on the growth of rice seedlings. Low FA concentrations (0.05 g/L) promoted rice seedling growth, whereas high FA concentrations (0.5 g/L) inhibited root growth, reduced cell activity and enzyme activity in the root tip, and accumulated reactive oxygen species in root cells. To investigate the underlying molecular mechanisms, we performed transcriptomic analysis and found that auxin (Aux) may participate in FA-mediated growth. Furthermore, transcriptome heatmap analysis showed a significant upregulation of the Aux/indoleacetic acid (Aux/IAA) gene family after FA treatment, suggesting that this gene family plays an important role in the effects of FA on root growth. Moreover, changes in endogenous Aux content and addition of exogenous Aux inhibitors confirmed the involvement of FA in rice seedling root growth and in the synthesis and transduction pathway of Aux. Conclusions This study demonstrated that the effects of FA on rice root growth may be achieved through the Aux synthesis and transduction pathway. We constructed a transcriptome landscape of the Aux synthesis and transduction pathway in FA-treated rice and identified a possible candidate gene family, IAA/Aux. These findings provide valuable clues for further understanding the mechanisms underlying the effects of FA on root growth in rice seedlings and offer new insights into the development of strategies for enhancing rice production.