Endogenous PttHb1 and PttTrHb, and heterologous Vitreoscilla vhb haemoglobin gene expression in hybrid aspen roots with ectomycorrhizal interaction

Abstract

Present knowledge on plant non-symbiotic class-1 (Hb1) and truncated (TrHb) haemoglobin genes is almost entirely based on herbaceous species while the corresponding tree haemoglobin genes are not well known. The function of these genes has recently been linked with endosymbioses between plants and microbes. In this work, the coding sequences of hybrid aspen (Populus tremula×tremuloides) PttHb1 and PttTrHb were characterized, indicating that the key residues of haem and ligand binding of both genes were conserved in the deduced amino acid sequences. The expression of PttHb1 and PttTrHb was examined in parallel with that of the heterologous Vitreoscilla haemoglobin gene (vhb) during ectomycorrhiza/ectomycorrhizal (ECM) interaction. Both ECM fungi studied, Leccinum populinum and Xerocomus subtomentosus, enhanced root formation and subsequent growth of roots of all hybrid aspen lines, but only L. populinum was able to form mycorrhizas. Real-time PCR results show that the dual culture with the ECM fungus, with or without emergence of symbiotic structures, increased the expression of both PttHb1 and PttTrHb in the roots of non-transgenic hybrid aspens. PttHb1 and PttTrHb had expression peaks 5 h and 2 d after inoculation, respectively, pointing to different functions for these genes during interaction with root growth-improving fungi. In contrast, ECM fungi were not able to enhance the expression of hybrid aspen endogenous haemoglobin genes in the VHb lines, which may be a consequence of the compensating action of heterologous haemoglobin.

Overexpression of spinach non-symbiotic hemoglobin in Arabidopsis resulted in decreased NO content and lowered nitrate and other abiotic stresses tolerance

“…NsHb1 is involved in various biotic and abiotic stress responses. For example, nsHb1 genes have been reported to be up-regulated by hypoxic, osmotic, and high salt 6 10 11 , short-term waterlogging 12 , treatments with salicylic acid, methyl jasmonic acid, ethylene, and H 2 O 2 13 , deficiency of phosphorus, potassium, and iron 8 , as well as dual culture with specific microsymbionts 14 . NsHb1 genes were also strong induced by nitrate, nitrite, or nitric oxide (NO) 15 16 .…”

Improving cellulase production in submerged fermentation by the expression of a Vitreoscilla hemoglobin in Trichoderma reesei

“…The bacterial hemoglobin (VHb) from the obligate aerobic bacterium Vitreoscilla is an oxygen-binding protein, functioning as an oxygen carrier and transporter (Wakabayashi et al 1986 ). In bacteria (Horng et al 2010 ), yeasts (Wu and Fu 2012 ), plants (Jokipii et al 2008 ) and animals (Pendse and Bailey 1994 ), the introduction of VHb has been proven to efficiently facilitate cellular aerobic metabolism, by which the growth rate and protein synthesis are improved under oxygen-limited conditions. Recently, examples have demonstrated that this strategy also works well in filamentous fungi.…”

Evolution, Three-Dimensional Model and Localization of Truncated Hemoglobin PttTrHb of Hybrid Aspen

“…According to our previous results, the PttTrHb expression was enhanced in roots of hybrid aspen ( Populus tremula L. × tremuloides Michx.) dual-cultured with ectomycorrhizal fungi [16] .…”

“…As bacterial TrHbs are known to detoxify NO [24] , Vieweg and co-authors [13] proposed that, similarly, the MtTrHb1 and MtTrHb2 proteins of M. truncatula (Mtr-HbO) could suppress NO accumulation during nodule and mycorrhizal symbioses. In our previous paper, we suggested that in hybrid aspen, PttTrHb may be involved in the modulation of NO levels in early reactions involved in root growth, in response to symbiosis with the ectomycorrhizal fungi [16] . In an A. thaliana mutant, the lack of the Ath-HbO protein inhibited the germination of seeds at elevated temperatures where the NO lifetime was increased and the germination restored with the addition of an NO scavenger, which suggests a potential role for TrHb as an NO scavenger [25] .…”

“…Previously, we have shown that hybrid aspen possesses two Hbs, PttHb1 and PttTrHb, and that PttHb1 is able to function in vivo as an NO scavenger with an applicable reductase [16] , [28] . The aim of the current study is to deepen the knowledge concerning PttTrHb by focusing on the protein 3D structure, phylogeny, localization and expression.…”