Plant hemoglobins: a journey from unicellular green algae to vascular plants

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 O 2 in nodules. The physiological roles of class 2 and class 3 Glbs are poorly defined but could involve O 2 and NO transport and/or metabolism, respectively. More research is warranted on these intriguing proteins to determine their non-redundant functions.

Lessons from the post-genomic era: Globin diversity beyond oxygen binding and transport

“…T1 chimeric and multi-unit globin sequences have been detected in ciliated protozoan parasites, while T1 and T2 single domain globins occur in microbial eukaryotes (ciliates, stramenopiles, oomycetes, opisthokonts, etc.) and in green algae [ 62 ]. In plants, only T2 single domain globins are present [ 62 , 63 ].…”

“…and in green algae [ 62 ]. In plants, only T2 single domain globins are present [ 62 , 63 ]. So far, there has been no report of T globins in metazoans.…”

Physiological significance of pedospheric nitric oxide for root growth, development and organismic interactions

“…The fine line between the revealed beneficial and toxic effects of NO during symbiosis, raises the demand for efficient spatial and temporal regulation of NO availability in nodules, and highlights the importance of its tight regulation for efficient symbiosis (Berger et al, 2019). In legumes, phytoglobins, both the prevailing symbiotic (SymPHYTOGB, Lb) and non-symbiotic isoforms (PHYTOGB 1 and 2), are known to represent key-players in the detoxification of excess NO in nodules due to their high affinity to NO (Becana, Yruela, Sarath, Catalan, & Hargrove, 2020). Recent studies in both major model legumes indicated a role of PHYTOGB1.1 in the modulation of NO content throughout the symbiosis.…”

Improving Air Quality by Nitric Oxide Consumption of Climate-Resilient Trees Suitable for Urban Greening

“…In fact, evidence exists that various enzymes have the ability to metabolize NO x . For example, phytoglobins (PGBs) are proteins regarded as important for the nitrogen metabolisms and are ubiquitously distributed in plants (Becana et al, 2020). These proteins play a major role in regulating many biological processes, such as normal growth and development, hypoxic stress, symbiotic nodulation and nitrogen fixation, and are activated in response to low mineral nutrient status and abiotic stress (Hebelstrup et al, 2006;Mira et al, 2016;Mira et al, 2017;Shankar et al, 2018;Becana et al, 2020;Berger et al, 2020).…”