Location: Wheat, Sorghum and Forage ResearchTitle: Plant hemoglobins: a journey from unicellular green algae to vascular plants
|BECANA, MANUEL - Estaciòn Experimental Aula Dei- Csic|
|YRUELA, INMACULADA - Consejo Superior De Investigaciones Cientificas (CSIC)|
|CATALAN, PILAR - University Of Zaragoza|
|HARGROVE, MARK - Iowa State University|
Submitted to: New Phytologist
Publication Type: Review Article
Publication Acceptance Date: 12/24/2019
Publication Date: 3/3/2020
Citation: Becana, M., Yruela, I., Sarath, G., Catalan, P., Hargrove, M.S. 2020. Plant hemoglobins: a journey from unicellular green algae to vascular plants. New Phytologist. Tansley review 1-18. https://doi.org/10.1111/nph.16444.
Interpretive Summary: Plant hemoglobins (Globins, Glb) are heme-containing red-colored proteins that have several known and unknown functions in plant cells. Based on their amino acid sequence and predicted protein folding patterns, they have been classified as 2/2 or 3/3 Glbs. Not much is known about the 2/2 Glbs in plants. The 3/3 Glbs contain 2 kinds of structures, the first, leghemoglobin, is related to the animal myoglobin and functions in transporting oxygen within plant cells, especially in the nitrogen-fixing root nodules. The other class of 3/3 Glbs, the hexcocordinated Glbs, do not function in oxygen transport, but appear to work by binding to small gaseous signaling molecules such as carbon monoxide (CO) and nitric oxide (NO). Recent studies have suggested distinct cellular roles for these hexcoordinated Glbs. Despite these new findings, there is still much to learn about these enigmatic plant proteins. In this review several aspects of plant Glbs are presented and discussed, and new areas of research are proposed.
Technical Abstract: Globins (Glbs) are widely distributed in archaea, bacteria and eukaryotes. They can be classified into proteins with 2/2 or 3/3 a-helical folding around the heme cavity. Both types of Glbs occur in green algae, bryophytes and vascular plants. The Glbs of angiosperms have been more intensively studied, and several protein structures have been solved. They can be hexacoordinate or pentacoordinate, depending on whether a histidine is coordinating or not at the sixth position of the iron atom. The 3/3 Glbs of class 1 and the 2/2 Glbs (also called class 3 in plants) are present in all angiosperms, whereas the 3/3 Glbs of class 2 have been only found in early angiosperms and eudicots. The three Glb classes are expected to play different roles. Class 1 Glbs are involved in hypoxia responses and modulate NO concentration, which may explain their roles in plant morphogenesis, hormone signaling, cell fate determination, nutrient deficiency, nitrogen metabolism and plant–microorganism symbioses. Symbiotic Glbs derive from class 1 or class 2 Glbs and transport O2 in nodules. The physiological roles of class 2 and class 3 Glbs are poorly defined but could involve O2 and NO transport and/or metabolism, respectively. More research is warranted on these intriguing proteins to determine their non-redundant functions.