Date of Graduation

7-2026

Document Type

Thesis

Degree Name

Master of Science in Cell & Molecular Biology (MS)

Degree Level

Graduate

Department

Cell & Molecular Biology

Advisor/Mentor

Srivastava, Vibha

Committee Member

Elli, Elvis

Second Committee Member

Sakon, Joshua

Keywords

AtDREB1a; Nitrogen use efficiency; OsDREB1C; Photosynthesis; Rice; Transgenic rice

Abstract

Rice is a globally consumed crop and feeds more than half of the world’s population. Nitrogen (N) fertilization is required for increasing rice crop production and yield, but producers often overuse N fertilizers, exceeding plant uptake capacity. Around 40% of the applied N is lost through volatilization and denitrification to the environment, causing algal bloom formation, greenhouse gas emissions, and water pollution. Therefore, improving nitrogen use efficiency (NUE) in rice has become a principal objective to achieve sustainable agriculture. NUE is a complex trait in rice that coordinates three processes: nitrogen uptake, transport and assimilation, which together support photosynthesis, biomass production, and grain yield. AtDREB1a is a transcription factor from Arabidopsis thaliana belonging to the AP2/ERF superfamily, which is known as a master regulator of abiotic stress responses such as drought, cold, and salinity. This study aimed to determine whether a transgenic line expressing AtDREB1a also improves nitrogen use efficiency by evaluating development and yield, through phenotypic and transcriptomic analyses. Phenotypic analyses during the vegetative growth revealed diverse responses in chlorophyll content, biomass production, and tillering. The transgenic line (TG) consistently showed higher chlorophyll content across N treatments (low, half, and normal), demonstrating that AtDREB1a drives enhanced chlorophyll content. Effects on biomass production and tiller number were limited and varied among environments and N conditions. Additionally, from the reproductive stage phenotypic analysis, TG line showed a slight increase in leaf N content at the R2 and R5 stage in the greenhouse, growth chamber, and hydroponic system, with the strongest effect under normal N conditions. Gas exchange parameters were also analyzed in the R3 stage, showing significantly higher photosynthetic rate, stomatal conductance, and transpiration in the TG line, especially under normal N conditions. Yield component analysis showed that the TG line produced more filled grain per plant, especially under normal N conditions. Transcriptomic analysis on 10-day-old seedlings showed a strong induction of the endogenous rice transcription factor OsDREB1C in the TG line, together with upregulation of photosynthesis-related genes and stress-responsive networks. OsDREB1C has been described as a regulator of NUE that activates nitrate transporters, photosynthesis-related genes, and early flowering (Wei et al., 2022). Therefore, the higher leaf N content, photosynthetic performance, and grain yield observed in the TG line are consistent with improved NUE and suggest an enhancement of N uptake, transport, and assimilation in the TG line, suggesting that AtDREB1a improves nitrogen use efficiency in rice possibly through the induction of OsDREB1C and the coordinated regulation of NUE-related physiological processes.

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