title: Nonsymbiotic hemoglobin-2 leads to an elevated energy state and to a combined increase in polyunsaturated fatty acids and total oil content when overexpressed in developing seeds of transgenic Arabidopsis plants.
abstract: Nonsymbiotic hemoglobins are ubiquitously expressed in plants and divided into two different classes based on gene expression pattern and oxygen-binding properties. Most of the published research has been on the function of class 1 hemoglobins. To investigate the role of class 2 hemoglobins, transgenic Arabidopsis (Arabidopsis thaliana) plants were generated overexpressing Arabidopsis hemoglobin-2 (AHb2) under the control of a seed-specific promoter. Overexpression of AHb2 led to a 40% increase in the total fatty acid content of developing and mature seeds in three subsequent generations. This was mainly due to an increase in the polyunsaturated C18:2 (ω-6) linoleic and C18:3 (ω-3) α-linolenic acids. Moreover, AHb2 overexpression led to an increase in the C18:2/C18:1 and C18:3/C18:2 ratios as well as in the C18:3 content in mol % of total fatty acids and in the unsaturation/saturation index of total seed lipids. The increase in fatty acid content was mainly due to a stimulation of the rate of triacylglycerol synthesis, which was attributable to a 3-fold higher energy state and a 2-fold higher sucrose content of the seeds. Under low external oxygen, AHb2 overexpression maintained an up to 5-fold higher energy state and prevented fermentation. This is consistent with AHb2 overexpression results in improved oxygen availability within developing seeds. In contrast to this, overexpression of class 1 hemoglobin did not lead to any significant increase in the metabolic performance of the seeds. These results provide evidence for a specific function of class 2 hemoglobin in seed oil production and in promoting the accumulation of polyunsaturated fatty acids by facilitating oxygen supply in developing seeds.
authors.affiliation: Genetics of Microorganisms, Department of Life Sciences, Institute of Botany, University of Liege, 4000 Liege, Belgium.
authors.forename: Helene
authors.initials: H
authors.lastname: Vigeolas
authors.forename: Daniela
authors.initials: D
authors.lastname: Hühn
authors.forename: Peter
authors.initials: P
authors.lastname: Geigenberger
mesh_terms: D017360:Arabidopsis / Q000187:drug effects / Q000196:embryology* / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000378:metabolism*; D004734:Energy Metabolism / Q000187:drug effects; D005231:Fatty Acids, Unsaturated / Q000378:metabolism*; D005285:Fermentation / Q000187:drug effects; D006454:Hemoglobins / Q000378:metabolism*; D009928:Organ Specificity / Q000187:drug effects / Q000235:genetics; D010100:Oxygen / Q000494:pharmacology; D010938:Plant Oils / Q000378:metabolism*; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic / Q000235:genetics; D012639:Seeds / Q000187:drug effects / Q000196:embryology / Q000235:genetics / Q000378:metabolism*; D013395:Sucrose / Q000378:metabolism; D013559:Symbiosis / Q000187:drug effects; D014280:Triglycerides / Q000378:metabolism; D017962:alpha-Linolenic Acid / Q000378:metabolism
chemical_list: C470347:AHB1 protein, Arabidopsis; C109042:AHB2 protein, Arabidopsis; D029681:Arabidopsis Proteins; D005231:Fatty Acids, Unsaturated; D006454:Hemoglobins; D010938:Plant Oils; D014280:Triglycerides; D017962:alpha-Linolenic Acid; D013395:Sucrose; D010100:Oxygen