Intrinsic non-symbiotic and truncated haemoglobins and heterologous Vitreoscilla haemoglobin expression in plants

Abstract

To date, haemoglobins (Hbs) have been shown to exist in all kingdoms of life. The least studied and understood groups are plant non-symbiotic haemoglobins (nsHbs) and the recently found plant truncated Hbs (trHbs). From a biotechnological point of view, the best characterized and almost exclusively applied Hb is the bacterial Vitreoscilla haemoglobin (VHb). In this review, the present state of knowledge of structural features and ligand binding kinetics of plant nsHbs and trHbs and their proposed roles as oxygen carriers, oxygen sensors, and for oxygen storage, in nitric oxide (NO) detoxification, and in peroxidase activity are described. Furthermore, in order to predict the functioning of plant Hbs, their characteristics will be compared with those of the better known bacterial globins. In this context, the effects of heterologous applications of VHb on plants are reviewed. Finally, the challenging future of plant Hb research is discussed.

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

“…Previous studies in this context were mainly focused on the heterologous expression of the bacterial Vitreoscilla hemoglobin in plants. This led to positive effects on growth and metabolism (Kallio et al, 2001(Kallio et al, , 2008Kallio, 2003, 2005;Jokipii-Lukkari et al, 2009) as well as on the production of different secondary metabolites in tobacco (Nicotiana tabacum; Holmberg et al, 1997), aspen (Populus spp. ; Häggman et al, 2003), and Arabidopsis (Wang et al, 2009).…”

“…; Häggman et al, 2003), and Arabidopsis (Wang et al, 2009). Although the underlying mechanisms are not fully resolved yet, Vitreoscilla hemoglobin is mainly considered as an oxygen-binding and -delivering protein with a possible function in facilitating oxygen supply (Jokipii-Lukkari et al, 2009).…”

Molecular Controls of the Oxygenation and Redox Reactions of Hemoglobin

“…Before O 2 was widely available, survival during anoxic/hypoxic interludes may have been enabled by the combined strong O 2 -binding and redox functionalities of Hbs and Mbs. It is intriguing in this regard that some nonsymbiotic plant Hbs enable sustained energy production under anaerobic/hypoxic conditions by exploiting a nicotinamide adenine dinucleotide (NADH) oxidase enzymatic function (9,66), similar to that of the flavohemoglobin (Hmp) of Escherichia coli (56). The combined O 2 -binding and redox functions of Hbs and Mbs play important roles in the tissues of current-day organisms (including many invertebrates) where hypoxic interludes are common (122), and protection against nitrosative stress is required (26).…”

Non-symbiotic hemoglobin and its relation with hypoxic stress

“…Since they were discovered, diverse biochemical and physiological functions have been attributed to plant hemoglobins, including the transport, storage, and sensing of oxygen. The nsHb have also been associated with the transport of ligands such as CO, NO, and fatty acids, as well as the function of an oxygen scavenger (ArredondoPeter et al, 1998;Jokipii-Lukkari et al, 2009;Thiel et al, 2011). Knock-out silencing studies in A. thaliana have demonstrated the fundamental role of nsHb during plant development, showing that at least one functional nsHb gene is essential for plant survival (Hebelstrup et al, 2006;Dordas, 2009).…”