Haydee Laza ^1* Bishwoyog Bhattharai ² Venugopal Mendu ³ Mark Burow ^1,4 Yves Emendack ⁵ Jacobo Sanchez ⁵ Aarti Gupta ¹ Mostafa Abdelrahman ¹ Lam-Son Phan Tran ¹ David Tissue ⁶ Paxton Payton ⁷

• ¹ Texas Tech University, Lubbock, United States
• ² University of Missouri, Columbia, Kentucky, United States
• ³ Montana State University, Bozeman, Montana, United States
• ⁴ Texas A&M AgriLife Research,Texas A and M University, Dallas, Texas, United States
• ⁵ Agricultural Research Service, Lubbock, TX 79415, USA., Lubbock, Italy
• ⁶ Hawkesbury Institute for the Environment, Western Sydney University, Penrith, New South Wales, Australia
• ⁷ Goanna Ag, Goondiwindi QLD 4390, Lubbock, United States

Elevated carbon dioxide [CO2] increases peanut carbon assimilation and productivity. However, the molecular basis of such responses is not well understood. We tested the hypothesis that maintaining higher photosynthesis under long-term elevated [CO2] is associated with the shift in C metabolism gene expression regulation. We used a field CO2 enrichment system to examine the effects of elevated [CO2] (ambient + 250 µmol m-2 s-1) across different soil water availability and plant developmental stages on the molecular responses in a peanut runner-type genotype. Plants under both [CO2] treatments were grown in semiarid conditions. We evaluated a comparative leaf transcriptomic profile across three periodic water deficit/re-hydration cycles throughout the growing season using RNA-Seq analysis. Our results showed that the transcriptome responses were influenced by [CO2], water availability, and developmental stages. The traditional Mercator annotation analysis based on percentage total revealed that lipid metabolism, hormone biosynthesis, secondary metabolism, amino acid biosynthesis, and transport were the most regulated biological processes. However, our new approach based on the comparative relative percentage change per individual category across stages revealed new insights into the gene expression patterns of biological functional groups, highlighting the relevance of the C-related pathways regulated by elevated [CO2]. The photosynthesis analysis showed that 1) the light reaction was the most upregulated pathway by [CO2] during water stress, 2) photorespiration was downregulated across all stages, 3) sucrose synthesis genes were upregulated by [CO2] before stress, 4) Starch synthesis genes were upregulated by [CO2] under drought periods, and 5) CO2 regulation of sucrose and starch degradation was critical under drought periods. Our findings provide valuable insights into the molecular basis underlying the photosynthetic acclimation response to elevated [CO2] in peanuts.