Auxin-Glucose Conjugation Protects the Rice (Oryza sativa L.) Seedlings Against Hydroxyurea-Induced Phytotoxicity by Activating UDP-Glucosyltransferase Enzyme

Vimalraj Kantharaj; Nirmal Kumar Ramasamy; Young-Eun Yoon; Mi Sun Cheong; Young-Nam Kim; Keum-Ah Lee; Vikranth Kumar; Hyeonji Choe; Song Yeob Kim; Hadjer Chohra; Yong Bok Lee

doi:10.3389/fpls.2021.767044

Auxin-Glucose Conjugation Protects the Rice (Oryza sativa L.) Seedlings Against Hydroxyurea-Induced Phytotoxicity by Activating UDP-Glucosyltransferase Enzyme

Front Plant Sci. 2022 Feb 16:12:767044. doi: 10.3389/fpls.2021.767044. eCollection 2021.

Authors

Affiliations

¹ Division of Applied Life Science (BK 21 Four), Gyeongsang National University, Jinju, South Korea.
² Department of Biotechnology, PSGR Krishnammal College for Women, Coimbatore, India.
³ Institute of Agriculture and Life Science (IALS), Gyeongsang National University, Jinju, South Korea.
⁴ Department of Smart Agro-Industry, Gyeongsang National University, Jinju, South Korea.
⁵ Division of Plant Sciences, University of Missouri, Columbia, MO, United States.

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.

Keywords: auxin; auxin conjugate; hydroxyurea (HU); reactive oxygen species (ROS); ribonucleotide reductase (RNR); uridine 5′-diphosphate-glucosyltransferase (UGT).