Genomic Science Program
U.S. Department of Energy | Office of Science | Biological and Environmental Research Program

Deciphering Genetic and Physiological Mechanisms of Nitrogen Use Efficiency in Camelina

Authors:

Demian Dlakic* (demian.dlakic@student.montana.edu), Maral Etesami, Samuel Decker, Andreas Fischer, Chengci Chen, Chaofu Lu

Institutions:

Montana State University–Bozeman

URLs:

Goals

Camelina (Camelina sativa) is a Brassica oilseed crop that has great potential to become a sustainable source of bioenergy in the U.S. However, the low nitrogen use efficiency and the low seed and oil yield compared to other major oilseed crops hinder this potential. The goal of this project is to decipher the genetic and physiological mechanisms that determine the nitrogen use efficiency and oilseed yield during the most critical processes of the camelina life cycle: (1) how camelina, in partnership with soil microbes, maximizes its ability to absorb and assimilate nitrogen into vegetative biomass; and (2) upon the transition to reproductive growth, how nitrogen is efficiently remobilized from senescing tissues (leaves and silicles) into sinks (seeds) to optimize yield potential by increasing seed size and enhancing oil synthesis.

Abstract

Enhancing oilseed yield with minimum nitrogen fertilizer input is a major pathway towards sustainable production of camelina oils. Researchers aim to obtain a systems-level understanding of genetic and physiological mechanisms that may be used to increase the nitrogen use efficiency (NUE) and to improve agronomic and seed traits in camelina.

First, field experiments were conducted to evaluate the genetic diversity of camelina performance and camelina responses to low and high nitrogen levels, and to determine the heritability of agronomic traits contributing to NUE. Evaluation of twenty selected varieties indicated significant genotypic variation in plant height, biomass, seed yield, and oil characteristics in both years of 2022 and 2023. While most varieties consistently demonstrated higher yields and oil content under high nitrogen (N) conditions, their responses to N fertilization differed, and several varieties showed low responses to N fertilization. Moreover, the consistently high heritability of traits and nitrogen uptake indicate that genetic variation plays a predominant role in shaping these characteristics over environmental factors. The field studies therefore demonstrated a wide variation of key agronomic traits in camelina, but also varied NUE. Camelina lines with different responses to N input were selected for further studies to decipher the genetic and physiological mechanisms of nitrogen utilization efficiency.

Second, genomics approaches were used to isolate genes that contribute to oil yield and NUE in camelina. A chromosome-level genome was assembled, based on which single nucleotide polymorphism (SNP) and insertion/deletion (InDel) markers were developed from resequenced genomes of the diversity panel consisting of 212 accessions of C. sativa (Li et al 2021). Agronomic traits including biomass, seed weight, seed oil content, and fatty acid composition were measured by growing in fields at two levels of N fertilization. Genome wide association studies (GWAS) identified quantitative trait loci (QTLs) for the above traits in both N treatments. Focusing on seed oil content, researchers found three QTL regions that explained 12 to 18% phenotype variance under low N conditions. To identify candidate genes within the QTLs, researchers analyzed transcriptomes of developing seeds in two camelina lines that differ significantly in their oil contents. A sucrose transporter was chosen as a candidate gene for further functional studies.

Third, nitrogen remobilization experiments were conducted to identify physiological mechanisms and genes controlling NUE in camelina. Nitrogen use of one variety (Suneson) was analyzed by growing plants hydroponically under either 6.5 mM (HN) or 0.65 mM nitrogen (LN). Nitrogen was either removed from the nutrient solution at anthesis or continued until plant maturity (four treatments). Nitrogen removal led to efficient remobilization from aboveground tissues to seeds, with N concentrations decreasing from ~4% to ~0.5% of tissue dry mass. N remobilization also occurred under HN-continued, but >2% remained at maturity, leading to substantial loss with plant residue. Seed N was at least 3% for all treatments, indicating that this concentration is necessary for viable seeds. In all treatments except HN-continued, the largest fraction of plant N is in seeds at maturity, demonstrating efficient nitrogen remobilization. Transcriptomics will be used to identify genes controlling nitrogen remobilization efficiency under the four different treatments.

References

Li, H., et al. 2021. “Genetic Dissection of Natural Variation in Oilseed Traits of Camelina by Whole-Genome Resequencing and QTL Mapping,” Plant Genome 14, e20110.

Funding Information

This research is supported by the U.S. DOE, Office of Science, BER Program, GSP grant no. DE-SC0021369.