Abstract
Hydroxyurea (HU) is the replication stress known to carry out cell cycle arrest by inhibiting ribonucleotide reductase (RNR) enzyme upon generating excess hydrogen peroxide (H2O2) in plants. Phytohormones undergo synergistic and antagonistic interactions with reactive oxygen species (ROS) and redox signaling to protect plants against biotic and abiotic stress. Therefore, in this study, we investigated the protective role of Indole-3-acetic acid (IAA) in mitigating HU-induced toxicity in rice seedlings. The results showed that IAA augmentation improved the growth of the seedlings and biomass production by maintaining photosynthesis metabolism under HU stress. This was associated with reduced H2O2 and malondialdehyde (MDA) contents and improved antioxidant enzyme [superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), and peroxidase (POD)] activity that was significantly affected under HU stress. Furthermore, we showed that the HU stress-induced DNA damage leads to the activation of uridine 5′-diphosphate-glucosyltransferase (UGT), which mediates auxin homeostasis by catalyzing IAA-glucose conjugation in rice. This IAA-glucose conjugation upregulates the RNR, transcription factor 2 (E2F2), cyclin-dependent kinase (CDK), and cyclin (CYC) genes that are vital for DNA replication and cell division. As a result, perturbed IAA homeostasis significantly enhanced the key phytohormones, such as abscisic acid (ABA), salicylic acid (SA), cytokinin (CTK), and gibberellic acid (GA), that alter plant architecture by improving growth and development. Collectively, our results contribute to a better understanding of the physiological and molecular mechanisms underpinning improved growth following the HU + IAA combination, activated by phytohormone and ROS crosstalk upon hormone conjugation via UGT.
Highlights
Plants, as sessile organisms, are constantly challenged by a wide range of environmental stresses that often cause crop or yield losses
The results showed that the root length was significantly decreased under HU stress compared to the control, whereas HU + Indole-3acetic acid (IAA) mitigated the root length reduction caused by HU and improved the root length compared to HU-treated plants (Figures 1A,B)
The plants treated with HU significantly reduced chlorophyll content, whereas IAA-treated plants had a slight increase than the control (Figure 1D)
Summary
As sessile organisms, are constantly challenged by a wide range of environmental stresses that often cause crop or yield losses. Reactive oxygen species (ROS) is an important signaling molecule that regulates plant growth and development in response to various stresses. Plants accumulate excess ROS, H2O2, which results in molecular, biochemical, and physiological damage due to over-oxidation of essential macromolecules such as DNA, protein, and membrane lipids by inhibiting ROS-scavenging enzymes (Das and Roychoudhury, 2014). Hydroxyurea (HU) is the DNA damage agent known to carry out cell cycle arrest by inhibiting the activity of ribonucleotide reductase (RNR) enzymes leading to an altered dNTP pool essential for DNA replication and cell cycle progression (Sakano et al, 2001; Cools et al, 2010; Winnicki, 2013). The RNRs are localized in the chloroplast, and the altered activity decreases the cell cycle, chlorophyll biosynthesis, and retarded growth (Juul et al, 2010; Gu et al, 2020)
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