Expression of the Tobacco Non-symbiotic Class 1 Hemoglobin Gene Hb1 Reduces Cadmium Levels by Modulating Cd Transporter Expression Through Decreasing Nitric Oxide and ROS Level in Arabidopsis

Abstract

Hemoglobin (Hb) proteins are ubiquitous in plants, and non-symbiotic class 1 hemoglobin (Hb1) is involved in various biotic and abiotic stress responses. Here, the expression of the tobacco ( Nicotiana tabacum ) hemoglobin gene NtHb1 in Arabidopsis ( Arabidopsis thaliana ) showed higher cadmium (Cd) tolerance and lower accumulations of Cd, nitric oxide (NO), and reactive oxygen species (ROS) like hydrogen peroxide (H 2 O 2 ). NtHb1 -expressing Arabidopsis exhibited a reduced induction of NO levels in response to Cd, suggesting scavenging of NO by Hb1. In addition, transgenic plants had reduced accumulation of ROS and increased activities of antioxidative enzymes (catalase, superoxide dismutase, and glutathione reductase) in response to Cd. While the expression of the Cd exporters ABC transporter (PDR8) and Ca 2+ /H + exchangers ( CAXs ) was increased, that of the Cd importers iron responsive transporter 1 ( IRT1 ) and P-type 2B Ca 2+ ATPase ( ACA10 ) was reduced in response to Cd. When Col-0 plants were treated with the NO donor sodium nitroprusside (SNP) and H 2 O 2 , the expression pattern of Cd transporters ( PDR8 , CAX3 , IRT1 , and ACA10 ) was reversed, suggesting that NtHb1 expression decreased the Cd level by regulating the expression of Cd transporters via decreased NO and ROS. Correspondingly, NtHb1 -expressing Arabidopsis showed increased Cd export. In summary, the expression of NtHb1 reduces Cd levels by regulating Cd transporter expression via decreased NO and ROS levels in Arabidopsis .

Low endogenous NO levels in roots and antioxidant systems are determinants for the resistance of Arabidopsis seedlings grown in Cd

“…ROS production has previously been shown to increase in different species including Arabidopsis in response to Cd, especially under long-term treatment conditions, both in adult plants (Gupta et al, 2017;Ortega-Villasante et al, 2007;Pérez-Chaca et al, 2014;Rodríguez-Serrano et al, 2006) and in seedlings (Kulik et al, 2012). H2O2 production has been shown to increase in the roots of 3-week-old Arabidopsis plants treated with 50 µM Cd (Bahmani et al, 2019), while H2S prevented this increase in 2-week-old seedling roots (Jia et al, 2016). However, in adult plants growing for three weeks under normal conditions and then treated with low concentrations of Cd, an increase in H2O2 was observed in both leaves and roots (Cuypers et al, 2011).…”

“…Therefore, NO needs to be tightly controlled in plant responses to Cd, as endogenous NO may increase metal uptake. Thus, overexpression of Nicotiana tabacum haemoglobin (NtHb1) in both tobacco and Arabidopsis plants, which down-regulate NO in response to Cd, was recently found to increase Cd tolerance, partly due to lower metal accumulation (Lee and Hwang, 2015;Bahmani et al, 2019). Furthermore, HY1 has been shown to increase Cd tolerance in Arabidopsis plants by reducing NO production and enhancing Fe homeostasis (Han et al, 2014).…”

Nitric oxide and hydrogen sulfide share regulatory functions in higher plant events

“…Likewise, NO and H 2 S can also interact with iron containing-proteins, where the metal is present as either heme group or as part of the iron-sulfur cluster. Thus, there are multiple examples in higher plants where either NO and H 2 S, or both, can modulate, through their interaction with the cysteine thiol groups, the functions of proteins such as cytochrome c oxidase, catalase, Fe-superoxide dismutase, ascorbate peroxidase, ferredoxin(Fd)-NADP reductase, glutaredoxin, Fd-dependent glutamine:2-oxyoglutarate aminotransferase (Fd-GOGAT) or phytoglobins, (Ramirez et al, 2011;Aroca et al, 2017;Bahmani et al, 2019;Niu et al, 2019;Corpas et al, 2021). These proteins are involved in essential plant processes including photosynthesis, respiration, antioxidant system, nitrogen and sulfur assimilation, which remarks the physiological relevance of these signaling molecules.…”

BrEXLB1, a Brassica rapa Expansin-Like B1 Gene Is Associated with Root Development, Drought Stress Response, and Seed Germination

“…Bra003006 encodes for a lipid-binding domain-START containing protein, while Bra001958 and Bra001852 encode non-symbiotic hemoglobin1 and cell wall-plasma membrane linker protein, respectively. Nonetheless, the studies on Bra001958 homologs found in other plants-including Arabidopsis-participate in cadmium tolerance (cd), detoxification of nitric oxide (NO), and reactive oxygen species, tolerance to abiotic stresses (e.g., salinity and osmotic stress) and pathogen attack [32]. A further in-depth study is essential to understand the role of Bra001852 and Bra003006 in BrEXLB1 mediated stress responses and growth regulation.…”