Plant hemoglobins: a journey from unicellulargreen algae to vascular plants

18 Pags.- 1 Tabl.- 7 Figs. © 2020 The Authors. Under Creative Commons License Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0).Globins (Glbs) are widely distributed in archaea, bacteria and eukaryotes. They can be classifiedinto proteins with 2/2 or 3/3 a-helical folding around the heme cavity. Both types of Glbs occur ingreen algae, bryophytes and vascular plants. The Glbs of angiosperms have been moreintensively studied, and several protein structures have been solved. They can be hexacoordinateor pentacoordinate, depending on whether a histidine is coordinating or not at the sixth positionof the iron atom. The 3/3 Glbs of class 1 and the 2/2 Glbs (also called class 3 in plants) are presentin all angiosperms, whereas the 3/3 Glbs of class 2 have been only found in early angiospermsand eudicots. The three Glb classes are expected to play different roles. Class 1 Glbs are involvedin hypoxia responses and modulate NO concentration, which may explain their roles in plantmorphogenesis, hormone signaling, cell fate determination, nutrient deficiency, nitrogenmetabolism and plant–microorganism symbioses. Symbiotic Glbs derive from class 1 or class 2Glbs and transport O2in nodules. The physiological roles of class 2 and class 3 Glbs are poorlydefined but could involve O2and NO transport and/or metabolism, respectively. More researchis warranted on these intriguing proteins to determine their non-redundant functions.Part of the work described in the lab of MB wasfunded by the Spanish Ministry of Science and Innovation-European Regional Development Fund (grant AGL2017-85775-R) and by Government of Aragón, Spain (group A09_17R).Peer reviewe